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Hey all, first time poster.
My Dad has a Dixon 4515B ZTR mower that he got from his nephew... yeah its about 20 years old, I believe it to be a 2000 model
It has a Vanguard 15.5hp OHV engine #28Q777-0691-E1 (photo attached)

It all started... thats how most projects begin right ... with repairing the mower deck where it was rusting out only in the front section, and I welded in new sheet metal and etc etc...

In any case, engine had an oil leak that had kept slowly getting worse, so wanted to get that fixed too. Appeared to be dipstick tube seal. Went to replace it, and when doing so I began cleaning all the old oil off the mower frame etc. Began to see oil going up the side of the block up under the engine cover, realized it must be the crankshaft seal under flywheel. Went to replace that, while doing so had the carb and air intake off. Happened to look into the intake side of the head and saw it was thickly coated in baked on oil . Long story short, ended up removing engine, complete tear down, found a thick layer of baked on oil (carbon buildup) all inside of head, top of piston, valves covered (not even sure if they were closing fully) etc. Oil in bottom of case was about a 1/2" of thick gel like sludge.The apparent problem was the bottom piston ring was stuck bad with a good amount of carbon build up, oil ring was stuck but came lose fairly easily when I began to mess with it.Top ring was moved ok, but there was build up in the groove. Seemed obvious that oil had been blowing by up into head.

After getting everything completely disassembled and several days worth of cleaning until all parts were spotless... all internal parts looked good. No scoring on cylinder sleeve nor piston, crank and cam had no scoring and no real wear, all teeth were sharp and square (not worn). Cam pressure release looked and operated just fine. Governor gearing was perfect, no wear, operated fine. etc etc .Got full engine gasket and seal kit, ring set, full carb rebuild kit including new float and float bowl (after cleaning found a tiny pin hole in old bowl). Rebuilt entire engine, including deglazing cylinder sleeve, lapping valves, as well as checking head and block for "flatness" using a slab of granite I keep in the shop. Used engine assembly lube on crank, cam, rod connector, pin, etc etc etc. Torqed everything to B&S specs as listed in their service manual, including the head in correct 3 rounds of increasing torque to final spec, and in correct order.

Reinstalled engine onto mower, and finished up installing carb, starter ect. Filled with conventional 10w30 oil and new B&S filter.
Took mower out for a short run, seemed to run good but not the power that it should have had. When engaging electric clutch for mower deck, engine bogged down significantly before coming back up to speed. When cutting any grass that was thick at all or "taller" than the rest, could hear the engine bog. At first thought maybe governor tab might needed adjusting (carb doesn't really have any adjustments but one) etc. Brought mower in and parked it as I didn't have the time that day.

Fast forward to two days ago, my Dad took mower out cut for about 20 min (just to test as grass isn't tall just beginning to grow), I could hear the mower bogging some as before etc. UPS truck shows up at our gate, my Dad drives down shuts mower off. UPS leaves, mower cranks but will not restart, doesn't even try to hit. I was in the shop, heard it, walked down to see what the problem was. Couldn't see any reason, thought maybe it either wasn't getting fuel or it was flooded. Tried some starter fluid in the air intake, nothing... must be flooded. Towed it back up to the shop. Started to pull plug when I noticed some fluid in the vacuum line going from crankcase breather to the fuel pump (I use the 1/4" silicone transparent fuel lines on anything I replace now days due to issues I've had with the old style lines, which is why I could see the fluid in the line). Took line off fuel pump, poured it out into my hand and it appears to be a mix of oil and gas. Ok... fuel pump membrane must have a hole in it. Checked oil, level was good and no indication of the presence of gas. Bought new fuel pump and air filter (even though the one on it was fairly new). Ran again... more fluid in vacuum line, but this time it was only oil.

Spoke again with Kevin who owns my local Stihl dealer, I buy most of my small engines parts, saws, etc from him as they are good people to work with and knowledgeable.The only other thing he (and myself) could think of is if the crank case breather spring was broke or something blocking it etc. Replaced crankcase breather with new. Ran again for a few min, line clear. Seemed like it fixed that issue, but engine still didn't have the power it should.

Today decided to recheck valve clearances, they were a bit off, and I will say they sure are touchy... finally was satisfied I had the clearances correct. Took mower out, power was much improved... but still bogged some. Wanted to run it longer, get engine up to full temp etc. Mowed about 20 min or so. Brought back into shop, oil was back in the vacuum line yet again, and engine would not restart.

I'm out of ideas... just doesn't make sense to me. If I hadn't just replaced the head gasket and etc, I would say a blown head gasket was possibly the issues. And that it was pushing a bit of pressure into crankcase. which in turn was pushing the oil through the breather. But I just did the headgasket with everything else with all brand new B&S parts.

Any input would be much appreciated

Edit: Just thought I would note that Italics button works, but "Bold" text doesn't appear to be working on here for some reason...

Some oil in the line to the fuel pump may be normal due to no way to stop oil from getting into the line.. the power issue and non restarting could be a partially sheared flywheel key.

Did you ever run this engine before tear down ? Sounds like it's been rode hard and put away wet. Maybe it's worn out. Bore Diameter 3.4365 in. (87.29 mm) / Bore reject 3.4395 in. (87.36 mm) / Bore Out-Of-Round .0015 in. (.04 mm)

Did you replace the fuel pump vacuum line with new "SAE J30 fuel hose" while you were re-assembling everything ? It's common that after 20 years this vacuum line has small leaks in it. Small leaks turn the vacuum hose into an impromptu "breather hose", and would allow crankcase oil into the hose. Small leaks in this hose will also keep the engine starved for fuel because the pump is not working with full pumping force. This would explain the engine's "low power" condition.

After 20 years on an air-cooled engine all your "rubber" parts are going to be shot. This list commonly includes hoses, o-rings and oil seals. First they harden. Then they crack. Then they leak.

With a 2000 engine it should have been mic'ed. Most likely the cylinder is both tapered and out of round which means that it need to go to .020 over if it was worn pass this. Just using a flex hone is also a mistake as it only makes things worst. Plus did you make sure you ordered the correct rings as they changed them in April 2001?

Side note the service manual still has the old cylinder torque spec of 220 in-lbs and the current torque spec is now 250 in-lbs. You also pay special attention the web area between the cylinder and the push rod galley as this where these engines blow head gaskets commonly.

Hi all thanks for the replies. Didn't get any emails that anyone had replied.
Anyway, try to answer everyone:

ILENGINE said:

Some oil in the line to the fuel pump may be normal due to no way to stop oil from getting into the line.. the power issue and non restarting could be a partially sheared flywheel key.

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I'm not sure how oil is the line is normal, I thought that is what the crank case breather was supposed to stop? Also if there is enough oil to block the line wouldn't that stop, or at least hinder, the vacuum to run the fuel pump? In which case would either cause no fuel to get through, or possibly cause the engine to run lean?
I tried my very best to assembly the flywheel and key very carefully, and torqued it to spec. I don't think that is the issue, as when it is cold, it starts right up fine. But I will look at it if I take the engine covers back off.

Bellcrank said:

Did you ever run this engine before tear down ? Sounds like it's been rode hard and put away wet. Maybe it's worn out. Bore Diameter 3.4365 in. (87.29 mm) / Bore reject 3.4395 in. (87.36 mm) / Bore Out-Of-Round .0015 in. (.04 mm)

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Yeah, we ran it for a couple seasons. Did all maintenance when we got it, and changed oil and filters regularly. Never saw the sludge and other until I took it apart though. My Dads nephew (my cousin) bought it from an auction... and yes there were issues from the beginning, but most seemed small and I was able to keep it running. The one that I couldn't fix was a light "knocking" or pinging sound. Part of it ended up being the spot welds holding the baffle inside the muffler had broke, I cut it open rewelded it, and welded the muffler back together (that was about 2 years ago when we first got it). Thought that had taken care of the sound, but could still hear a light pinging coming from the crankcase. It doesn't seem to have this sound now though. The bore being out of spec could be possible. I didn't measure it, as I didn't really have any tool that could do so. A T-Bore hole gauge would have worked, but don't have one and didn't realize at the time that some cheapos could be found.

Born2Mow said:

Did you replace the fuel pump vacuum line with new "SAE J30 fuel hose" while you were re-assembling everything ? It's common that after 20 years this vacuum line has small leaks in it. Small leaks turn the vacuum hose into an impromptu "breather hose", and would allow crankcase oil into the hose. Small leaks in this hose will also keep the engine starved for fuel because the pump is not working with full pumping force. This would explain the engine's "low power" condition.

After 20 years on an air-cooled engine all your "rubber" parts are going to be shot. This list commonly includes hoses, o-rings and oil seals. First they harden. Then they crack. Then they leak.

Click to expand...

I did replace the vacuum line, as well as all other fuel lines. But not with SAE hose, I used transparent silicone fuel hose. Thats why I could see the oil in the line. With oil going into that line, I also thought that it blocking the vacuum to the fuel pump could be part of the power issues. I did replace all gaskets, all seals, and etc with all brand new. As you said, 20 years old all those type parts are going to be hard and cracking.

StarTech said:

With a 2000 engine it should have been mic'ed. Most likely the cylinder is both tapered and out of round which means that it need to go to .020 over if it was worn pass this. Just using a flex hone is also a mistake as it only makes things worst. Plus did you make sure you ordered the correct rings as they changed them in April 2001?

Side note the service manual still has the old cylinder torque spec of 220 in-lbs and the current torque spec is now 250 in-lbs. You also pay special attention the web area between the cylinder and the push rod galley as this where these engines blow head gaskets commonly.

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The new rings were the correct part number as per the engine date code according to B&S, and they are B&S brand rings too. I didn't even know they sold oversized rings for these... manual never mentioned it and I hadn't replaced rings on a small engine before. Yeah, I should have found a way to measure the cylinder bore. As I said up above, didn't have the tools, didn't know I could have gotten some cheap, and also there are no machine shops out here so had no where to get it measured either.
I didn't know about the torque spec change, I'll have to go look at the service manual I have and see the spec it gave, as that is the torque I set it too. And if I remember right, I *believe* it was 220. If that it what the manual I have states, I'll step it up to the 250 see what that does. I had thought about going higher recently, but didn't want to strip the threads out of the block. If they raised the torque spec, then compression leakage is most likely why they would have done so.
And yes that web area is the weakest point of these OHV gaskets. Just replaced one on another mower that I got for free as it would put out a literal cloud of smoke that you couldn't see through (due to the blown head gasket), and that is exactly where it blew out too. That mower doesn't have a mower deck, but since fixed it works great to pull my yard trailer I built

Additional Question: Is there a way to know if the muffler is partially blocked??? I read somewhere that this could cause similar issues. But it appears that the exhaust flow is normal. I may just pull the muffler off and see what happens.

Thanks for all the input and information everyone. I will go through some of these tomorrow if I have time to work on it. Once I go through the list, I'll report back if anything changed for better or worse.

The only thing I had clogged mufflers on has been 2 cycles but anything can happen.

Yes the manual wasn't written with a novice in mind. If in the rear you will find that if cylinder has .004" of wear over the standard cylinder size you need to hone it to .020 over. As said this cant done with a flex but is instead done using a rigid hone with the correct stones. Ridge hones prevents the stones from just following the current taper and/or oval.

Aluminum cylinders 280 grit (nothing of coarser grit). Cast iron lined 180 grit (can use 80 grit for quick take to near .015 over then switch to 180 grit). You must create a crosshatch pattern of 45 degrees. Also while honing keep the rpm down under 300 rpm especially with aluminum to prevent galling and use honing oil. Smaller the diameter the slower.


If it does comes to oversizing then you will need both the OS piston and ring set.

warreng5995 said:

I did replace the vacuum line, as well as all other fuel lines. But not with SAE hose, I used transparent silicone fuel hose. That's why I could see the oil in the line. With oil going into that line, I also thought that it blocking the vacuum to the fuel pump could be part of the power issues. I did replace all gaskets, all seals, and etc with all brand new.

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• No experience with that type hose, but even if it only lasted a month there should be no vacuum leaks and the "low fuel delivery due to loss of vacuum" reduced to a non-issue. Still could be a tiny hole in the pump's diaphragm, but the I agree the hose should be 100% fixed. Good call.
• Oil in the clear hose is not a sign of anything, other than that the hose is connected to the engine's sump.

That's all I got.

StarTech said:

The only thing I had clogged mufflers on has been 2 cycles but anything can happen.

Yes the manual wasn't written with a novice in mind. If in the rear you will find that if cylinder has .004" of wear over the standard cylinder size you need to hone it to .020 over. As said this cant done with a flex but is instead done using a rigid hone with the correct stones. Ridge hones prevents the stones from just following the current taper and/or oval.

Aluminum cylinders 280 grit (nothing of coarser grit). Cast iron lined 180 grit (can use 80 grit for quick take to near .015 over then switch to 180 grit). You must create a crosshatch pattern of 45 degrees. Also while honing keep the rpm down under 300 rpm especially with aluminum to prevent galling and use honing oil. Smaller the diameter the slower.

View attachment 55788View attachment 55789
If it does comes to oversizing then you will need both the OS piston and ring set.

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I've rebuilt car engines and such, so I understand the procedures. I also did a bit of research on the differences for a small engine as well. I just wasn't going to go have it bored out if it was off. But I should have measured it to see how far out of spec it was, as if it was too far then I should have just junked the mower. The only reason I even did the engine rebuild, is because of all the other work I had already put into the mower.

Born2Mow said:

• No experience with that type hose, but even if it only lasted a month there should be no vacuum leaks and the "low fuel delivery due to loss of vacuum" reduced to a non-issue. Still could be a tiny hole in the pump's diaphragm, but the I agree the hose should be 100% fixed. Good call.
• Oil in the clear hose is not a sign of anything, other than that the hose is connected to the engine's sump.

That's all I got.

Click to expand...

Its the type of line often used on trimmers, chainsaw, etc. They just use a much smaller size. In any case, I know there may be oil vapor/residue in the line. But I think I'm getting so much oil in the line that it is slowing the vacuum to the fuel pump. With the engine off, there is about 1" of oil (in length) in the lowest part of the line. In any case, if that's not the issue then hopefully its one of the other things that I can fix.

Ok, a bit of an update.
I looked at the vacuum line today and about 1.5 to 2 inches of it was filled with oil (see first photo attached). ILENGINE & Born2Mow both of you said oil in the line may be normal. So I figured ok, lets not drain the line and leave the oil there and try to start it and see what happens. With the choke on, cranked it over and it fired right up.

So, I figured I might as well as pull the dipstick and see how much pressure it was pushing. Pulled the dipstick, and a light spray of oil did come out until I put my hand and paper towel over it. I could feel some air but didn't seem more than what I thought would be normal. After holding the paper towel over it for 5 or 10 seconds, I removed it and replaced the dip stick. There was some oil spray on the towel, but not soaked or anything. Oil level has stayed at the full mark this whole time.

Just for a comparison, I went out back to my other mower with B&S (16.5hp) and did the same thing. it actually sprayed more oil into my paper towel than this one did. But I am pretty sure it doesn't have a oil pump (but is "splash lube" only - I could be wrong about this though) as it doesn't have an oil filter like this engine does.

Back to this Vanguard, I ran the engine and let it come up to full temp, I watched the head and some other points with a infrared "laser" thermometer to see if I could find any abnormal hot spots. The hottest point on the head was near the spark plug, with temps around 280 to 300 f. The hottest spot I could find on the muffler was 680F at one point. Most of the muffler was around 450 to 500 f. Oil filter stayed between 122 and 130 f, as did the crankcase next to the filter. Valve cover got up to about 135 f. Other parts of the head and case were much cooler due to the air flow from the flywheel "cooling fan". I think the float bowl on the carb was around 110 f.
I will add there is no odd sounds or anything. It doesn't surge or etc. Runs smoothly.

Now that it was at full temp, I pulled the dipstick again and the air and oil spray seemed exactly the same as when I first started it. So no difference there.

Finally I turned off engine... let it sit for about 2 minuets or so. Tried to restart, it didn't want to, it chugged a bit, I let off the key and it chugged a few more times on its own but then picked back up to normal engine speed. So I ran it a few more minutes, and turned it off again. This time i let is sit about 5 minutes. Tried to restart, Nothing. Didn't even try to hit. Tried to restart it a few more times, letting it sit a minute or two between attempts, but never hit. Same as it did the other day.

I didn't have any more time to mess with it today, so that's all I was able to test.
But in short, it appears that the oil in the vacuum line isn't the issue, as it was that way today when I started the engine cold, and it fired right up just fine. So I guess that part is "solved" and appears to be a non-issue.

At this point, I don't think I'm getting piston blow by or bypass on the head gasket. As cold and hot both seemed to be the same with my mediocre "dip stick test".
I can't do a proper compression test on this engine, because it has the compression release on the cam shaft so it is easier to start. Which this compression release "lobe" doesn't move out of the way until the engine is running and the centrifugal force moves it. So from what I can see and understand, due to this compression release the compression PSI will never show correctly when just cranking the engine over. If anyone can confirm or refute this, please feel free to post such.

With that said, I did check my service manual StarTech and it listed 220 in-lbs as you said the old versions did. So when I have the time to pull the covers, intake/carb and etc. I may up the torque on the head to 250 in-lbs as per your suggestion.

So in the end with what little I was able to "test" today.... Why does the engine start cold just fine and seems to run "normally" and smoothly... but once hot when you shut it down for a few min, it won't restart?? Could this still be an issue with compression? Vapor lock in carb, but only after the engine cools?? Or...??? ?

Thanks All

Question. When it doesn't restart, does it spin normally while cranking?

StarTech said:

Question. When it doesn't restart, does it spin normally while cranking?

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Yep, no hard turn over or anything. It just cranks and cranks, but doesn't even try to hit.
When cold, it starts and runs fine... until you turn it off for 5 min.
Before I re-adjusted the valves it had a very noticeable amount of power loss under load, but after the last adjustment power is improved (although its still less than it should be).

I just thought about something... what if its just a coincidence?? What I mean is, what if it not restarting when hot doesn't have anything to with the rebuild itself... and instead the issue just happened to occur during the time period of this rebuild?
Most of the time I really dismiss anything as "coincidence"... but what if the coil is breaking down?? Starts fine when cold... but once the engine is hot, the coil could be overheating to the point it has weak spark when hot??? It has to have some spark or it wouldn't run at all when the engine is hot. But once you turn the engine off, and the engine cools down enough. It takes a full powered spark to restart, but if the coil is still too hot and still has a weak spark, you get a hot engine no start condition???

Does this seem plausible? Anyone have a opinion?

Spend $ 20 & get a red in line spark tester
No flashing = dud coil or kill wire shorting
Remove will wire from coil
Flashes red = short in wiring or faulty safety switch.
If it only does it when the blades are on suspect the reverse switch.

The oil is colleting in your vacuum line due to the sag. The line should run downhill from the fuel pump into the fitting on the breather to prevent oil pooling in the line. I am wondering if you are not loosing spark when the engine gets hot. heat sinking the ignition module.

bertsmobile1 said:

Spend $ 20 & get a red in line spark tester
No flashing = dud coil or kill wire shorting
Remove will wire from coil
Flashes red = short in wiring or faulty safety switch.
If it only does it when the blades are on suspect the reverse switch.

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its not switches nor kill wire.
starts and runs when cold, continues to run when hot. After its hot, if you turn off engine for 5 minutes, it won't Re-Start.

ILENGINE said:

The oil is colleting in your vacuum line due to the sag. The line should run downhill from the fuel pump into the fitting on the breather to prevent oil pooling in the line. I am wondering if you are not loosing spark when the engine gets hot. heat sinking the ignition module.

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ok, i'll try to see if there is a way to re-run the line. the carb and choke rods are in the way.
ignition module, possible. hadn't thought about that either. its mounted on a "plate" via one of the starter bolts.

warreng5995 said:

ok, i'll try to see if there is a way to re-run the line. the carb and choke rods are in the way.
ignition module, possible. hadn't thought about that either. its mounted on a "plate" via one of the starter bolts.

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The ignition module is what you are calling the coil. Don't confuse it with the regulator/rectifier for the charging system which could be located next to the starter.

warreng5995 said:

Why does the engine start cold just fine and seems to run "normally" and smoothly... but once hot when you shut it down for a few min, it won't restart?? Could this still be an issue with compression? Vapor lock in carb, but only after the engine cools?? Or...??? ?

Click to expand...

In my experience this is due to coating of the jets.

The EPA has made all engine builders lean out their engines. This started this about 1988. They have gotten progressively leaner in stages, which is why many motorcycles now have fuel injection. If they have their way, look for electronic fuel injection on mowers in the next 10 years, or all-electric mowers mandated by law.

When everything is "perfect" your engine is running on a very minimal amount of fuel. Should anything happen to the float level or the jet size, then there won't be enough fuel to start a hot engine without using the choke.

Enter ethanol loaded fuels. When these are left in the carb for any length of time, the alcohol attracts water. The alcohol and water mixture leaves a very thin layer of (usually dark brown) "varnish" on everything.... including the inside of the jets. This makes the jet smaller on its fuel metering orifice... which in turn further leans out the fuel mixture. It's not much, but it's enough. The engine seems to run correctly, but it's really starved for fuel. Thus, the only way a hot engine will start is by using the choke.



Since the engine seems to run OK, I wouldn't open the carb. In your shoes I'd start using a "fuel stabilizer" AND carb cleaner, such as StarTron. The stabilizer will work to prevent future problems by keeping the alcohol in solution with the gasoline, and the cleaner will work to clean out any varnish that has accumulated. And it will do this while you run the engine on your regular schedule.

I implement this plan in my shop by treating the fuel in the BIG cans as soon as I bring it home from the gettin' place. In this way the StarTron works its way into my chain saw, leaf blower, weed whacker, my Exmark and both my walk-behinds. And the plan works. None of my equipment ever has carb or fuel issues.

Hope this helps.

Fuel injection via throttle bodies is already here especially on v-twins. Briggs, Kawasaki, and Kohler all have fuel injected engines. Even Robin/Subaru even tried it on singles years ago. An example of the Robin is the EX21-EFI which they finally reverted back carburetors because they had so much problems with it.

Born2Mow said:

In my experience this is due to coating of the jets.

The EPA has made all engine builders lean out their engines. This started this about 1988. They have gotten progressively leaner in stages, which is why many motorcycles now have fuel injection. If they have their way, look for electronic fuel injection on mowers in the next 10 years, or all-electric mowers mandated by law.

When everything is "perfect" your engine is running on a very minimal amount of fuel. Should anything happen to the float level or the jet size, then there won't be enough fuel to start a hot engine without using the choke.

Enter ethanol loaded fuels. When these are left in the carb for any length of time, the alcohol attracts water. The alcohol and water mixture leaves a very thin layer of (usually dark brown) "varnish" on everything.... including the inside of the jets. This makes the jet smaller on its fuel metering orifice... which in turn further leans out the fuel mixture. It's not much, but it's enough. The engine seems to run correctly, but it's really starved for fuel. Thus, the only way a hot engine will start is by using the choke.

Since the engine seems to run OK, I wouldn't open the carb. In your shoes I'd start using a "fuel stabilizer" AND carb cleaner, such as StarTron. The stabilizer will work to prevent future problems by keeping the alcohol in solution with the gasoline, and the cleaner will work to clean out any varnish that has accumulated. And it will do this while you run the engine on your regular schedule.

I implement this plan in my shop by treating the fuel in the BIG cans as soon as I bring it home from the gettin' place. In this way the StarTron works its way into my chain saw, leaf blower, weed whacker, my Exmark and both my walk-behinds. And the plan works. None of my equipment ever has carb or fuel issues.

Hope this helps.

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Fully agree about the ethanol and the EPA garbage. I wish the carbs were adjustable again... what the stupid EPA has forced to be done to them is as stupid as the new "no spill" fuel cans... along with many other things.
As far as ethanol goes, I don't buy ethanol fuel just for some of the reasons you listed. My local gas station is also a truck stop and they sell premium non-ethanol gasoline. Back about 5 years ago when I did buy ethanol, and even though I put some type of stabilizer in it, I kept having issues with my trimmers and chainsaw carbs, even a carb on a very small genset. Clean and rebuilt them, last for a while same issues. Bought new carbs, after a while, same issues. Switched to non-ethanol, haven't had any more problems.

I do use fuel stabilizer in anything engine that doesn't get used often or is going to be sitting more than a couple weeks. Also used it in the storage can if the fuel isn't going to be used directly. Haven't heard of startron before. But I do not like "stabil", its garbage in my opinion. I found a stabilizer called PRI-G for gasoline and PRI-D for diesel. Have used both for several years and it works well. From what I remember reading several years ago, its the same company that makes fuel stabilizer used in most ships.

In any case, like I said in my op, just got done with this full engine rebuild, full carb rebuild including all new jets, float, etc. I haven't ran the engine probably 1 hour in total since rebuild. All fresh fuel, clean tank, all new filters, new fuel pump, new fuel lines, new plug, etc.
Also the first time it wouldn't restart when hot (the first real time running it after rebuild), my Dad had tried it out for about 20 min cutting and shut it down when the UPS guy showed up. When it wouldn't restart I also thought it wasn't getting fuel, so I got some started fluid and shot it in the air intake, got nothing, not even a hit. Just like all the other times since when hot. So at that point I thought maybe the needle valve got stuck or something and might have flooded while he was talking to the UPS guy, towed it back up to the shop pulled plug, little glaze on the plug. cranked over engine, mist shot out of cylinder, but nothing out of the ordinary. So thats when I started trying to figure out what was going on before I ever posted here. Which at that time I thought it was related to the oil in the vacuum line going to the fuel pump, but have since ruled that out as a non-issue.

With that said, I could be wrong, but I really think its a weak coil at this point. When I get some time, I'm going to take the coil out and go buy a new B&S one from my local Stihl dealer. So we'll see what that does. I don't like throwing parts at an engine and see what sticks, but after everything else I've already rebuilt and replaced on this thing, might as well replace the coil too.

StarTron was originally developed for boaters. As much trouble as Ethanol caused in mowers and trimmers, it nearly killed the pleasure boat industry due to the proximity of water 24/7. It's a stabilizer AND cleaner, which is far better than a simple stabilizer, like Stabil. As long as you're already buying a fuel additive, it certainly wouldn't hurt to try a different one. It's certainly no more costly.

This is not a comment on your carb rebuilding skills. Please don't take it that way. What I'm saying is that carbs made in the last 15 years are VERY complex instruments, with as many as 4 stages of jetting for a variable-speed engine. It's extremely difficult for anyone to clean all the passageways without an ultrasonic cleaner and a tremendous amount of time.

I really hope the new coil fixes your issue. But if not, then maybe you'll remember this post.

All the best.

Born2Mow said:

StarTron was originally developed for boaters. As much trouble as Ethanol caused in mowers and trimmers, it nearly killed the pleasure boat industry due to the proximity of water 24/7. It's a stabilizer AND cleaner, which is far better than a simple stabilizer, like Stabil. As long as you're already buying a fuel additive, it certainly wouldn't hurt to try a different one. It's certainly no more costly.

This is not a comment on your carb rebuilding skills. Please don't take it that way. What I'm saying is that carbs made in the last 15 years are VERY complex instruments, with as many as 4 stages of jetting for a variable-speed engine. It's extremely difficult for anyone to clean all the passageways without an ultrasonic cleaner and a tremendous amount of time.

I really hope the new coil fixes your issue. But if not, then maybe you'll remember this post.

All the best.

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no offense taken ?, carb bodies are something else to clean sometimes with all the tiny passages and such, and it does take a good amount of time to clean and rebuild them. Smaller the carb the worse they are. But have been using an ultrasonic cleaner in recent years, which does help a lot. Besides the sonic cleaning itself, I also like usings its heater to warm up the distilled water (which I always use when cleaning carbs as I have well water) pretty good, as that seems to help clean a lot better too. Add in some sonic cleaner "soap" and I also add in some Mean Green Industrial Strength (which is difficult to find these days) when ever I'm cleaning carbs, and all together it does a pretty good job. I usually run a carb through several 30 min cycles (as 30 min is the longest cycle my cleaner will set for...?), just depending on what else I'm doing in the shop or how quickly I need the carb done. Then when it comes out of the cleaner, I use my air compressor to blow out all the passages.
I'm no pro by any means, I've just learned over the years what works for me, as I repair all my own stuff, whether it is mowers, 2-cycles, motorcycle, or cars/trucks. Can't afford to pay someone else to do it. And tbh I'd rather do most things myself, at least I know what was actually done... even if I do it wrong the first time and figure it out later, maybe then I'll know how to fix it lol ?

warreng5995 said:

Hi all thanks for the replies. Didn't get any emails that anyone had replied.
Anyway, try to answer everyone:


I'm not sure how oil is the line is normal, I thought that is what the crank case breather was supposed to stop? Also if there is enough oil to block the line wouldn't that stop, or at least hinder, the vacuum to run the fuel pump? In which case would either cause no fuel to get through, or possibly cause the engine to run lean?
I tried my very best to assembly the flywheel and key very carefully, and torqued it to spec. I don't think that is the issue, as when it is cold, it starts right up fine. But I will look at it if I take the engine covers back off.


Yeah, we ran it for a couple seasons. Did all maintenance when we got it, and changed oil and filters regularly. Never saw the sludge and other until I took it apart though. My Dads nephew (my cousin) bought it from an auction... and yes there were issues from the beginning, but most seemed small and I was able to keep it running. The one that I couldn't fix was a light "knocking" or pinging sound. Part of it ended up being the spot welds holding the baffle inside the muffler had broke, I cut it open rewelded it, and welded the muffler back together (that was about 2 years ago when we first got it). Thought that had taken care of the sound, but could still hear a light pinging coming from the crankcase. It doesn't seem to have this sound now though. The bore being out of spec could be possible. I didn't measure it, as I didn't really have any tool that could do so. A T-Bore hole gauge would have worked, but don't have one and didn't realize at the time that some cheapos could be found.


I did replace the vacuum line, as well as all other fuel lines. But not with SAE hose, I used transparent silicone fuel hose. Thats why I could see the oil in the line. With oil going into that line, I also thought that it blocking the vacuum to the fuel pump could be part of the power issues. I did replace all gaskets, all seals, and etc with all brand new. As you said, 20 years old all those type parts are going to be hard and cracking.


The new rings were the correct part number as per the engine date code according to B&S, and they are B&S brand rings too. I didn't even know they sold oversized rings for these... manual never mentioned it and I hadn't replaced rings on a small engine before. Yeah, I should have found a way to measure the cylinder bore. As I said up above, didn't have the tools, didn't know I could have gotten some cheap, and also there are no machine shops out here so had no where to get it measured either.
I didn't know about the torque spec change, I'll have to go look at the service manual I have and see the spec it gave, as that is the torque I set it too. And if I remember right, I *believe* it was 220. If that it what the manual I have states, I'll step it up to the 250 see what that does. I had thought about going higher recently, but didn't want to strip the threads out of the block. If they raised the torque spec, then compression leakage is most likely why they would have done so.
And yes that web area is the weakest point of these OHV gaskets. Just replaced one on another mower that I got for free as it would put out a literal cloud of smoke that you couldn't see through (due to the blown head gasket), and that is exactly where it blew out too. That mower doesn't have a mower deck, but since fixed it works great to pull my yard trailer I built

Additional Question: Is there a way to know if the muffler is partially blocked??? I read somewhere that this could cause similar issues. But it appears that the exhaust flow is normal. I may just pull the muffler off and see what happens.

Thanks for all the input and information everyone. I will go through some of these tomorrow if I have time to work on it. Once I go through the list, I'll report back if anything changed for better or worse.

Click to expand...

I had two mowers that had oil coming back to the carburator and in each the float valve was stuck and the gas was filling the crankcase and forcing the oil out.

Reading the posts, couldn't find any reference to the having done a compression test. When the new rings were put in, did the cylinder show scoring? As someone suggested, I would hook up spark tester and run it. Look for any signs of missing or poor ignition. Also, I would check for oil breather for blockage or sludge.

donens2018 said:

Reading the posts, couldn't find any reference to the having done a compression test. When the new rings were put in, did the cylinder show scoring? As someone suggested, I would hook up spark tester and run it. Look for any signs of missing or poor ignition. Also, I would check for oil breather for blockage or sludge.

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The problem is these engines have an ACR which limits the compression to 60-90 psi. In order to get a valid compression reading ti would require adjust the vavle clearance until the ACR is no longer effective. But there is one problem that as the electric starters are too weak to turn the engine through the compression stroke. Briggs recommends doing leak down tests instead when a compression problem is suspected.

JMK1038 said:

I had two mowers that had oil coming back to the carburator and in each the float valve was stuck and the gas was filling the crankcase and forcing the oil out.

Click to expand...

The clear fuel line you are using going to the fuel pump might be some of your problem! This line will collapse and therefore won't work for the fuel pump correctly! That fuel line should be a ridged black double core rubber line. If it collapses it will not operate the fuel pump correctly!

ezcruisn71 said:

The clear fuel line you are using going to the fuel pump might be some of your problem! This line will collapse and therefore won't work for the fuel pump correctly! That fuel line should be a ridged black double core rubber line. If it collapses it will not operate the fuel pump correctly!

Click to expand...

Snowmobiles use the same type of fuel pump and they will not work correctly with the clear fuel line either.

I'm pretty sure there's a Reed valve under the flywheel that goes bad and that's why you have oil in the vacuum tube.

ezcruisn71 said:

Snowmobiles use the same type of fuel pump and they will not work correctly with the clear fuel line either.

Click to expand...

The fuel line I am talking about comes off the Engine. It is the pulse line to the pump. This must be dual core rubber line. The other lines can be clear line

My kawasaki Mule uses a vacuum pump, i have the clear line on it and it works great.
Polyuerthane

Did we do a leak-down on this?

So your engine crankcase is getting pressure inside it from somewhere. As oil is splashed around inside, that increase in pressure is pushing oil through the breather line that goes to your fuel pump. So, where can the pressure come from? Well, as the piston moves up and down, it creates positive and negative pressures in there. This is usually relatively low pressure differences because the size of the crankcase and the distance of the piston motion. Any oil usually goes through breather and back into engine through galley.

So, in your case, I'm guessing as the piston goes to top of stroke to compress fuel/air mixture (or exhaust stroke as well), and some of that is getting by and pressurizing the crankcase - loss of power also. If that engine has a oil filler tube, you may feel the blow-by. How does it get past? Either the, as you said, the head gasket, valves not closing, or the rings. Harbor Freight has a cheap cylinder pressure tester. I dunno the specs but seems 90 to 120ish psi should be good.

I'd do a leak down test next.
Good luck

JMK1038 said:

I had two mowers that had oil coming back to the carburator and in each the float valve was stuck and the gas was filling the crankcase and forcing the oil out.

Click to expand...

yep, as I said that in some previous posts, I thought about that at one point. But the oil isn't being thinned down, don't see or smell any fuel in the oil either.

donens2018 said:

Reading the posts, couldn't find any reference to the having done a compression test. When the new rings were put in, did the cylinder show scoring? As someone suggested, I would hook up spark tester and run it. Look for any signs of missing or poor ignition. Also, I would check for oil breather for blockage or sludge.

Click to expand...

Sdmcarlson said:

So your engine crankcase is getting pressure inside it from somewhere. As oil is splashed around inside, that increase in pressure is pushing oil through the breather line that goes to your fuel pump. So, where can the pressure come from? Well, as the piston moves up and down, it creates positive and negative pressures in there. This is usually relatively low pressure differences because the size of the crankcase and the distance of the piston motion. Any oil usually goes through breather and back into engine through galley.

So, in your case, I'm guessing as the piston goes to top of stroke to compress fuel/air mixture (or exhaust stroke as well), and some of that is getting by and pressurizing the crankcase - loss of power also. If that engine has a oil filler tube, you may feel the blow-by. How does it get past? Either the, as you said, the head gasket, valves not closing, or the rings. Harbor Freight has a cheap cylinder pressure tester. I dunno the specs but seems 90 to 120ish psi should be good.

I'd do a leak down test next.

Good luck

Click to expand...

As I said in previous posts, my Dad bought this mower from his nephew who bought it from an auction.... We ran it for a couple seasons, but there always seemed to be something I had to fix all the time to keep it running. Fast forward, I basically have rebuilt the entire mower. Including a complete full engine rebuild, hasn't been run maybe an hour.
When I first broke it down, yes there was a lot of sludge in the bottom of the sump pan. But after breakdown I spent several days cleaning **everything**, including the whole crankcase, nearly spotless. So no sludge now.

I also have replaced crankcase breather, fuel pump, air filter, fuel filter, oil filter, fuel lines, rings, all gaskets and seals, sparkplug, valves lapped, complete rebuild on carb, and probably some more things that I can't remember right now. All parts are all B&S OEM. (except the fuel pump that I just replaced a few days ago while troubleshooting is an Oregon)
The fuel tank was also removed and cleaned out.

After I readjusted the valves again this last time, and spent like an hour doing so before I was completely satisfied.The power was decently improved from what it was, but its not 100%.

lefty2cox said:

Did we do a leak-down on this?

Click to expand...

StarTech said:

The problem is these engines have an ACR which limits the compression to 60-90 psi. In order to get a valid compression reading ti would require adjust the vavle clearance until the ACR is no longer effective. But there is one problem that as the electric starters are too weak to turn the engine through the compression stroke. Briggs recommends doing leak down tests instead when a compression problem is suspected.

Click to expand...

Yep, what StarTech said above, Can't do a compression test on this engine, as it has a compression release built into the camshaft to make it easier to start. That compression release doesn't move out of the way until centrifugal force overcomes it when the engine is running. So using a compression tester only gives a false reading at best.

Leak down test is possible, haven't done that yet. Might try it when I get time.

Also Cylinder and piston were clean, no scoring at all. New B&S rings.

sterobinson said:

I'm pretty sure there's a Reed valve under the flywheel that goes bad and that's why you have oil in the vacuum tube.

Click to expand...

humm... don't remember seeing any valve or opening under the flywheel, other than the crankshaft seal of course. The vacuum line goes to the crankcase breather, which I also just replaced, but it is on the side of the case down toward the bottom behind the carb.

ezcruisn71 said:

The clear fuel line you are using going to the fuel pump might be some of your problem! This line will collapse and therefore won't work for the fuel pump correctly! That fuel line should be a ridged black double core rubber line. If it collapses it will not operate the fuel pump correctly!

Click to expand...

ezcruisn71 said:

Snowmobiles use the same type of fuel pump and they will not work correctly with the clear fuel line either.

Click to expand...

ezcruisn71 said:

The fuel line I am talking about comes off the Engine. It is the pulse line to the pump. This must be dual core rubber line. The other lines can be clear line

Click to expand...

I know the vacuum line. I thought about that, watched and felt of it with engine running and didn't see any flexing of the line at all. If I didn't have a clear line on there, I wouldn't even know there was any oil in the line to begin with. Further, with the engine running, the oil seems to stick back only on the walls of the line, fuel pump runs fine. I may change the line to a regular black fuel hose just to see if there is a difference in running, have no way to see inside a regular black fuel line to see if the oil is still present though.
At this point I think this is a non-issue, and was mostly just my observation of not seeing it before because I had been running a regular black hose fuel line previously.

At this point my main issue is, it will start when engine is cold every time, it will continue to run even after engine is hot and up to full temp. But once you turn the engine off, and leave it off for around 5 min or so, it won't restart. Doesn't even hit, and I've ruled out "not getting fuel". And it is getting air. So its either compression or spark.

With that said I believe it is a weak ignition coil. Although its working, and will start a cold engine, when the coil itself is also cold. Once the engine gets hot and the coil is hot, when the engine cools down some the coil is still too hot and has a weak spark. And therefore doesn't have a strong enough spark to restart the "cooler" engine.
It will however restart a Hot engine. As in have the engine running up to full temp. Turn off engine, wait only a few seconds, restart engine. But if the engine sits for 5 min or so, it won't restart until its basically cold.

So a weak coil is my theory. We'll see what happens. I don't have a spark tester at the moment, but I am getting one. I have removed plug previously and reconnected the coil wire to it, grounded plug back to the block and cranked the engine, it does have spark. Just how strong of a spark when the coil is hot is the question..?
As soon as I get time I'm going remove cover and etc, remove coil and go buy a new one. I've replaced about everything else anyway, might as well replace the coil too as it may even be the original for all I know.

When I get time, I will try to do a leak down test and see what results that gets.

Thanks Everyone for All the Info and Replies! ?
Will update when I have more

That's High crank case pressure due to blow by on the rings. So its worn rings, or ring clearance. That would account for the oil leak from the dipstick as well. Oil cannot travel up the vacuum line to the pump any other way. It also accounts for the oil on the intake as well from the crank case breather. Oil would only pass here if the breather valve was stuck open or crank case pressure was raised.

You also must know you cannot replace rings in a worn barrel as the barrel will be oval and the rings round. Hence blow by. So unless you have checked the barrel for round, honed the barrel even new rings will not seal.

HOLY COW. I am surprised by the responses.

I run a repair shop, and am a Briggs master technician. you are describing a typical problem. so typical, i could not believe the responses. you have too much crankcase pressure. normally, at a shop, we hook up a crankcase pressure gauge at the dip stick to see what the pressure is. the tool is called a manometer. the crankcase needs to show negative pressure (a vacuum) and, you are describing all of the typical symptoms of positive pressure. there are a few things that cause that, but the most likely suspect is a blown head gasket. second would be a breather valve that's not working, and third would be blow by past the rings, but that's the most rare.

BTW, i have worked on perhaps 1000 machines in the last year.

the crank case is building up pressure, and forcing oil out of all sorts of places. if i was a betting type, I'd bet its a head gasket.

Brian - Modern Mower said:

HOLY COW. I am surprised by the responses.

I run a repair shop, and am a Briggs master technician. you are describing a typical problem. so typical, i could not believe the responses. you have too much crankcase pressure. normally, at a shop, we hook up a crankcase pressure gauge at the dip stick to see what the pressure is. the tool is called a manometer. the crankcase needs to show negative pressure (a vacuum) and, you are describing all of the typical symptoms of positive pressure. there are a few things that cause that, but the most likely suspect is a blown head gasket. second would be a breather valve that's not working, and third would be blow by past the rings, but that's the most rare.

BTW, i have worked on perhaps 1000 machines in the last year.

the crank case is building up pressure, and forcing oil out of all sorts of places. if i was a betting type, I'd bet its a head gasket.

Click to expand...

I think he said in the original post that the head gasket and breather were both replaced.

Thanks for the replies and info guys, will take all into account ?

Here is my Update: Over the last several days when I had a few min, I made a leak down tester. So this morning with the engine cold, put the engine to TDC, placed vice grips on the crankshaft against the frame so the engine could not move. Pulled the spark plug and it was a bit wet, appeared to be oil.
Screwed in my compression hose, and with the air compressor regulator set at 100psi, the leak down gauge showed about 80psi or so. And I could hear the air coming out somewhere.

So I got to searching, first thing I did was pull the dipstick and put my ear up to the fill tube. But the air leak wasn't any louder. So I kept searching and found the sound was louder on the other side of the engine around the carb/intake area. At first I thought it was coming from around the head gasket, but it sounded higher up. So I pulled the air filter cover and filter off, and the sound was definitely louder, and I could see a film of oil down in the bottom of the air intake "tube" where its takes in the air through the filter.

So, I put everything back together, put my spark test on and started the engine. Good steady spark.
Turned off engine, took off spark tester, restarted and went and mowed for about 20 min to put a load on the engine and get it up to full temp.

Brought it back in, shut it down, pulled spark plug. Plug looked clean and dry this time (of course engine was hot too). Reinstalled Leak Down tester, removed air filter. When I connected the tester to the compression hose, once again tester showed 80psi. And I could hear air coming up through the intake, and saw some smoke this time coming up through the intake, and once again there was oil in the bottom of the air intake "tube".

So that's a 20% loss of compression. But a hot or cold engine didn't make a difference in pressure loss, it was the same both times. Which to me would appear its not the rings???

With the engine still hot, I then reinstalled the plug with spark tester again, and the spark was still strong and steady, the same as it was with the engine cold. So I was wrong about a weak coil apparently.

With that said, after engine was at full temp and shut down. When I attempted to restart, the engine will chug a bit at first, but then comes up to speed, when it does I did notice it puffed smoke for a second or so. It did this every time except the first time when I first shut it down, that time it would not restart. But I even went back out and mowed for another 20 min, brought it back in and shut it down. But once again it would chug for a few hits but then come up to speed with a couple puffs of smoke.

So I couldn't figure out why I couldn't replicate the the hot-no start issue now when it would do it every time last week.

Today I checked the oil again when it was cold before I did anything this morning and it was at the full mark.
After running it and the engine was hot, after I shut it down and did the leak down tests and etc. I once again checked the oil level and this time the oil was Over Full. If the "low to full" mark is 8oz as is written on the stick. Then it appears it may now be another "8oz" OVER full.
Which must mean fuel is getting into the oil/crankcase. And if so, this *may* be why the engine restarts now even when hot, as there is enough fuel in the oil to make it combust easier?? IDK
OR would the oil expand this much simply due to the engine being hot/overheated due to the intake valve leak? I wouldn't think so and haven't seen this before personally, nor heard of it before either. But you all would know more. I will have to go back and check oil level again once engine is cold to verify its still showing over full.

In any case at the very least, this currently seems to show that the intake valve is leaking. The only way that I know of to verify this would be to pull the head and do a "liquid leak" test, with the head upside down and held in a vice or etc, and cover the valves in a liquid (such as gas or carb cleaner) and see if the liquid would leak past the valve. If so, then it means the valve is not sealing and it also show which valve is leaking. Which again if this is the issue it would have to be the intake.

But I'm not sure how this would be forcing a film of *oil* back up into the air intake? (the new intake valve seal???)
And also apparently getting fuel into the crankcase?? (will recheck oil level to verify this)

I got to thinking about the intake valve as I was walking back over the house, and this may have been what was wrong originally before I rebuilt the engine. As if the intake valve was not sealing, and somehow this was forcing oil back up into the intake, which would then mean it was also being drawn into the combustion chamber where it would be burned. Would this not be the cause of why the intake valve, piston and inside of head had such a thick coat of baked on oil/carbon?? The exhaust valve I might say had some carbon on the face of the valve, but not much around the seal or the back of the valve. The intake valve on the other hand was really bad, as well as the intake port in the head.

So with all that said, I have a 20% pressure leak through the intake valve. Some oil coming up through the air intake and apparently being burned in combustion. And very possibly fuel going into the crankcase.

What do you guys think???

EDIT: Just wanted to add, as I stated in previous posts, I lapped the valves during the rebuild and they appeared to have seated well all the way around. BUT could the valve be bent just slightly enough to cause this?? Or maybe I just thought I had them seated good. Been a while since I lapped valves on a car engine.

EDIT 2: Rechecked oil level after engine was cold. It is back down to the Full mark.

You indicated that you checked the oil after doing a leak down. This may sound like a dumb question but did you clean the dipstick and then check it? Or just pull the stick and check it? Some air always gets by the piston during leak-down and pressurizing the crankcase will force oil up the stick.

Most on here are wiser than I am but if you have fuel in the oil and are losing air through the intake, you have two problems. The intake valve and leaking carb, I would think. Did the oil smell like fuel? 8 oz is enough to make a stink I would imagine.

lefty2cox said:

You indicated that you checked the oil after doing a leak down. This may sound like a dumb question but did you clean the dipstick and then check it? Or just pull the stick and check it? Some air always gets by the piston during leak-down and pressurizing the crankcase will force oil up the stick.

Most on here are wiser than I am but if you have fuel in the oil and are losing air through the intake, you have two problems. The intake valve and leaking carb, I would think. Did the oil smell like fuel? 8 oz is enough to make a stink I would imagine.

Click to expand...

yep, checked oil level when engine cold and it was at full mark. Checked again when it was hot, it was over full. But then checked it again later after engine cold, and it was back down to the full mark. And yes I always clean the dipstick off first
I looked at the oil and smelled of it, but no it didn't smell like gas which surprised me seeing it was showing over full at the time. But like I said, it went back down the full mark after the engine cooled, so I don't know. never seen this happen before. the only guess i have is because of the intake valve leaking, it could be causing the engine to overheat and make the oil 'expand'... or cause air to get trapped somewhere making it look like the oil level had risen??? idk

warreng5995 said:

Hey all, first time poster.
My Dad has a Dixon 4515B ZTR mower that he got from his nephew... yeah its about 20 years old, I believe it to be a 2000 model
It has a Vanguard 15.5hp OHV engine #28Q777-0691-E1 (photo attached)

It all started... thats how most projects begin right ... with repairing the mower deck where it was rusting out only in the front section, and I welded in new sheet metal and etc etc...

In any case, engine had an oil leak that had kept slowly getting worse, so wanted to get that fixed too. Appeared to be dipstick tube seal. Went to replace it, and when doing so I began cleaning all the old oil off the mower frame etc. Began to see oil going up the side of the block up under the engine cover, realized it must be the crankshaft seal under flywheel. Went to replace that, while doing so had the carb and air intake off. Happened to look into the intake side of the head and saw it was thickly coated in baked on oil . Long story short, ended up removing engine, complete tear down, found a thick layer of baked on oil (carbon buildup) all inside of head, top of piston, valves covered (not even sure if they were closing fully) etc. Oil in bottom of case was about a 1/2" of thick gel like sludge.The apparent problem was the bottom piston ring was stuck bad with a good amount of carbon build up, oil ring was stuck but came lose fairly easily when I began to mess with it.Top ring was moved ok, but there was build up in the groove. Seemed obvious that oil had been blowing by up into head.

After getting everything completely disassembled and several days worth of cleaning until all parts were spotless... all internal parts looked good. No scoring on cylinder sleeve nor piston, crank and cam had no scoring and no real wear, all teeth were sharp and square (not worn). Cam pressure release looked and operated just fine. Governor gearing was perfect, no wear, operated fine. etc etc .Got full engine gasket and seal kit, ring set, full carb rebuild kit including new float and float bowl (after cleaning found a tiny pin hole in old bowl). Rebuilt entire engine, including deglazing cylinder sleeve, lapping valves, as well as checking head and block for "flatness" using a slab of granite I keep in the shop. Used engine assembly lube on crank, cam, rod connector, pin, etc etc etc. Torqed everything to B&S specs as listed in their service manual, including the head in correct 3 rounds of increasing torque to final spec, and in correct order.

Reinstalled engine onto mower, and finished up installing carb, starter ect. Filled with conventional 10w30 oil and new B&S filter.
Took mower out for a short run, seemed to run good but not the power that it should have had. When engaging electric clutch for mower deck, engine bogged down significantly before coming back up to speed. When cutting any grass that was thick at all or "taller" than the rest, could hear the engine bog. At first thought maybe governor tab might needed adjusting (carb doesn't really have any adjustments but one) etc. Brought mower in and parked it as I didn't have the time that day.

Fast forward to two days ago, my Dad took mower out cut for about 20 min (just to test as grass isn't tall just beginning to grow), I could hear the mower bogging some as before etc. UPS truck shows up at our gate, my Dad drives down shuts mower off. UPS leaves, mower cranks but will not restart, doesn't even try to hit. I was in the shop, heard it, walked down to see what the problem was. Couldn't see any reason, thought maybe it either wasn't getting fuel or it was flooded. Tried some starter fluid in the air intake, nothing... must be flooded. Towed it back up to the shop. Started to pull plug when I noticed some fluid in the vacuum line going from crankcase breather to the fuel pump (I use the 1/4" silicone transparent fuel lines on anything I replace now days due to issues I've had with the old style lines, which is why I could see the fluid in the line). Took line off fuel pump, poured it out into my hand and it appears to be a mix of oil and gas. Ok... fuel pump membrane must have a hole in it. Checked oil, level was good and no indication of the presence of gas. Bought new fuel pump and air filter (even though the one on it was fairly new). Ran again... more fluid in vacuum line, but this time it was only oil.

Spoke again with Kevin who owns my local Stihl dealer, I buy most of my small engines parts, saws, etc from him as they are good people to work with and knowledgeable.The only other thing he (and myself) could think of is if the crank case breather spring was broke or something blocking it etc. Replaced crankcase breather with new. Ran again for a few min, line clear. Seemed like it fixed that issue, but engine still didn't have the power it should.

Today decided to recheck valve clearances, they were a bit off, and I will say they sure are touchy... finally was satisfied I had the clearances correct. Took mower out, power was much improved... but still bogged some. Wanted to run it longer, get engine up to full temp etc. Mowed about 20 min or so. Brought back into shop, oil was back in the vacuum line yet again, and engine would not restart.

I'm out of ideas... just doesn't make sense to me. If I hadn't just replaced the head gasket and etc, I would say a blown head gasket was possibly the issues. And that it was pushing a bit of pressure into crankcase. which in turn was pushing the oil through the breather. But I just did the headgasket with everything else with all brand new B&S parts.

Any input would be much appreciated

Edit: Just thought I would note that Italics button works, but "Bold" text doesn't appear to be working on here for some reason...

Click to expand...

Make sure that air filter is halfway clean. If the engine can't pull in fresh air through the filter, it'll suck it up through the crankcase breather hose. I've seen this a few times. Just a suggestion.

Megalosdog said:

Make sure that air filter is halfway clean. If the engine can't pull in fresh air through the filter, it'll suck it up through the crankcase breather hose. I've seen this a few times. Just a suggestion.

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Yep, already got a new filter and pre filter foam screen

warreng5995 said:

EDIT: Just wanted to add, as I stated in previous posts, I lapped the valves during the rebuild and they appeared to have seated well all the way around. BUT could the valve be bent just slightly enough to cause this?? Or maybe I just thought I had them seated good. Been a while since I lapped valves on a car engine.

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Some ideas...

• You can't lap the valves and get 100% contact on the valve and the seat if the valve is bent. You could have the adjuster on the intake valve too tight, or your valve timing can be off, thus forcing the valve to leak.
• You stated you ran this test at TDC. But you did not state which TDC. There are 720 deg of crankshaft rotation in one full cycle of a 4-stroke engine. Novices often forget that with 2 full turns, the piston comes to TDC twice in that 720 deg, but the valves can only be adjusted at every other TDC. At one TDC both rockers should be tight (both valves slightly open). At the next TDC both valves are fully closed (both rockers loose). It's only this last TDC when you can adjust the valve clearance and do pressure testing.

Hope this helps.

Born2Mow said:

Some ideas...

• You can't lap the valves and get 100% contact on the valve and the seat if the valve is bent. You could have the adjuster on the intake valve too tight, or your valve timing can be off, thus forcing the valve to leak.
• You stated you ran this test at TDC. But you did not state which TDC. There are 720 deg of crankshaft rotation in one full cycle of a 4-stroke engine. Novices often forget that with 2 full turns, the piston comes to TDC twice in that 720 deg, but the valves can only be adjusted at every other TDC. At one TDC both rockers should be tight (both valves slightly open). At the next TDC both valves are fully closed (both rockers loose). It's only this last TDC when you can adjust the valve clearance and do pressure testing.

Hope this helps.

Click to expand...

Good points. As far as the valve being adjusted to tight, I know I did have a time with getting them set, at least to my satisfaction. With that said, both valve rocker arms were loose before I began to adjusting them.
If the valve was bent, I certainly couldn't tell it after I inspected them or when lapping. But I was just trying to think of any reasons that the intake valve would be leaking. And I had my crank and cam timing marks lined up when I reassembled the engine.

Alright... Here's the "update"...

today I removed the valve cover, then removed the rocker arms and rods. This eliminates it being the valves being adjusted wrong (which they still might have been off a bit), then after doing this I performed another leak down test. 100psi in, once again about 80 to 85 psi held in cylinder. Which again means 15 to 20% loss. But this time, there wasn't any air coming out the intake ... but I could still hear it blowing out somewhere, and after reaching in I could feel the air with my fingers at the head gasket between the cylinder and valve passage. I did retorque all the head bolts, which is at the 250 in lbs that StarTech said it had been updated to in the newer manuals. And tested it again, but it Made Zero Difference.

Kept looking, tried to see if I could find air coming out somewhere else etc. As I just couldn't figure why the headgasket would be bad, as its brand new. Finally I gave up, removing everything to get down to the head, and pulled the head. I expected to find... Something... Anything that would explain the pressure loss.
But Instead all I found was a thin film of oil in the bottom of the cylinder. Everything else, including the head gasket, looked perfect. I even took the head itself and sit it in a vice and did a "liquid leak" test on the valves with some WD-40, but it never leaked a bit. Letting it sit overnight just for the heck of it. Still not sure why air was leaking the other day through the air intake, unless I still didn't have the valves set right...

In anycase, I used a machined straight edge (which is about 1/2" wide) that is rated to be flat to .001 (1 thousandth), and I laid it across the section of the head between the cylinder and push rod area. The thinnest feeler gauge I have is a .0015 and it wouldn't even try to slide under. I also used a bright light behind the straight edge while I looked from the other side, and couldn't see any light underneath of it. Any sort of deviance THAT small should certainly be taken up by the headgasket!


So I don't know guys, its leaking out from a brand new head gasket without any obvious reason...When I work on anything... even building/fabricating, repair work, cars, tractors, whatever... I always try to do everything "the right way"... but I'm about to the point I'm going to do it the "country way". I am just about ready to get some JB Weld and coat each side the gasket, and slap this stupid thing back together and let it setup for a day or two. And if that doesn't "fix" it... I'm going to sell it for parts or whatever I can get out of it. I've already wasted FAR to much time and $ this past winter on this dixon, and my patients is just about out, as the weather has already broken and I've got other work that I've got to get to. Just need to get a cow and let it eat the grass... save me the time of cutting it...

I have seen others write about getting bad head gaskets, which leak latterly. You might try a new gasket and check for leaks?

SHB said:

I have seen others write about getting bad head gaskets, which leak latterly. You might try a new gasket and check for leaks?

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its looks perfect... but you're right it still may just be a bad gasket. I'll take your advice and try another gasket, one last time.

QUESTION: I know on a car, you should never be able to spin/turn the valves in the head by hand. But what about in a briggs engine? with the valves installed in the head, I can apply a little pressure with my fingers to the "face" of the valve and turn it. is this normal for a mower engine? Or does this mean the springs are weak??

ok... after disassembly i re-lapped the valves again... just to make sure. then cleaning everything down with brake and carb cleaner. I reinstalled valves. Using my thumb on face of valves, the exhaust valve I can turn it a bit. but I cant turn the intake valve. but nothing has any oil on it right now.

thought I would post some pics of the end result of what I said in my previous post. i also included a close up of the head between cylinder and rod passageway where it was leaking during leak down test. maybe someone sees something that I dont for the reason of the compression leak.

PS: I also put my straight edge machined to a flatness rating of .001 on the block across the section between cylinder and rod passageway. couldn't get a .0015 feeler gauge to slip under at all. also used light shines behind it, couldn't see any light from other side. so I don't think cylinder or block is warped or anything. going to buy another new gasket and see what that does.

well, replaced headgasket with another brand new one... did leakdown test... now @ 100psi in... 70psi holding in cylinder. so a 30% loss, 10% worse than it was before...