Engine Starved for Gas

ILENGINE said:

First order of business, I ran the 691035 filter on gravity flow engines for years without issues, so don't worry about the fuel pump rating. I went back to the 394358S filter after 2012 because it was causing issues with the filtration level not allowing enough flow with the new run under slight tank vacuum EPA vent on the tank.

You said the slope may be significant in your yard. Do you have any way to measure the slope. I am wondering, and this is just a wild though. The angle is causing the fuel to run to one side of the fuel bowl causing it to have a high enough level to burn the fuel out of the carb enough to get the main jet out of the fuel in the carb.

The other thought is the opposite of fuel starvation, and the slope is causing the fuel bowl vent to get flooded with fuel causing a rich run issue.

Just throwing some random thoughts out there for consideration.

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New "first order of business" is Thank you so much for taking the time to lend your expertise and insight.
So, if I understand you correctly, the 691035 fuel filter will probably work fine in my machine, but the real factory spec filter is 394358S? I will probably return the former and exchange it for the latter.

I went out a few minutes ago and used a couple of carpenter's levels, tape measure and some trigonometry to come up with an approximation of the slope of the backyard at its steepest pitch. I got about 12 degrees. Most of the yard is probably half that down to about level.
I am skeptical about the fuel flooding for a couple of reasons. First, the engine sputtering subsides when I see the fuel enter the empty filter. Also, the sputtering begins when the slope of the terrain tilts the fuel tank away from the engine.
As I say; I'm skeptical, but I am not ready to discard completely any reasonable possibility.
Chartman

bertsmobile1 said:

If it works every time from full to 3/4 then it is definately a fuel supply problem.
The pressure head is not enough to unseat the float needle.
Is this the same carb that the mower came with.
Fuel pumps run about 3 to 7 psi which while not much, is more than the pressure from a gravity head.
Gravity feeds use coarser filters than pressure fed ones.

Have a close look at the needle in the float and the seat.
Chances it is sticking a little.

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Hi bertsmobile1. Thanks again for working with me on this problem.
I bought this lawn tractor used last year. There is nothing I see that suggests to me that the carburetor has been replaced, or even tampered with; but I cannot say for sure.
I think your suggestion of a sticky float needle is a good one. I haven't had the pleasure of disassembling the carb on this unit so far, but it seems like it might be in my near future.
I think it may be possible to get at those parts without removing the whole carb. It probably should not be done over the grass.
I will get the proper fuel filter as suggested by Ilengine.
I don't suppose this engine can be retrofitted for a fuel pump?
I am also wondering about that solenoid shutoff to prevent backfiring. It was awfully hot at the end of the mowing. I think there is a spring loaded needle that shuts off fuel flow to the engine unless the solenoid is pulling it open. Solenoids sometimes fail or weaken under high temperature. What if I just remove that spring so it stays open? I normally stop the engine by shutting off the fuel valve, so backfiring might not be an issue.
Chartman

I thought you had already done the carb.
A little problem remembering exactly who has done what.
You will find the instructions for the carb here http://outdoorpowerinfo.com.

The shut off solenoid works by jambing a bung into the end of the main jet which stops any fuel getting into the engine instantly.
Down here they are not an EPA requirement so we just snip them off.
You can replace it with a short bolt for the purpose of elimination however in some places you ca get massive fines for tampering with it.
They do occasionally cause intermittent problems if the wires are broken at the terminal.

The fact that it only happens when the tank is 1/3 full or less still sounds like a pressure head problem or a restriction.

Boudreaux In Eunice La. said:

Ok in between my wife talking to me and trying to read all these post's...... I will comment .....

I agree with IL Engine about the filters...... I use the 691035 filters all the time on regular 8 HP Briggs and Techs the same size ......

The 691035 is a 40 Micron filter which is smaller than the 394358S filter which is 75 Microns. Not smaller in size, but smaller in the fact that it catches smaller particles of debris........

The 394358S is a small white filter and the other is a clear see thru filter.......And much bigger......

I did see see where you blew thru all the passages and then let the fuel flow from the tank into a container with no issue........

BUT even with NO fuel pump no matter what filter you have on there, the engine still works the same way with or without a fuel pump.... The engine sucks air into the carb via the intake stroke on a regular gravity feed tank..... With a fuel pump the engines are bigger and usually have bigger carbs and fuel usage / consumption.... So there is 2 ways to get more fuel to the carb and the piston / pistons.......

The only thing I can suggest is that your fuel lines are [flapping] on the inside...... Ethanol has took it's toll on them, and it don't take long... 1 month or 2 years ????

Even though you did empty the tank in a jar without the cap on or off doesn't mean anything.......... The fuel system is still under pressure with the carb doing it's normal work..... Even without the pump like I said earlier....

You got me curious though on not a see thru shut off valve ..... I have some in stock 698183 and bust a pack open and check that out and reply in a lil while ...........

Let us know Mon Ami ~!~!

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Hi Boudreaux. Thanks for taking the time to help me out!
It sounds to me like you think that the suction from the engine may be causing the rubber fuel lines to collapse because they have been degraded by the ethanol in the gas.
Hmmmm. They seemed to be pretty rigid as I was cleaning and blowing them out. I'll give them a squeeze next time they are hot and see what I think. I assume the remedy would be to replace those rubber lines. I do have some fresh stock.
I am confused by the fuel filter references. The filter I have, but did not install, is the 691035; a 40 Micron filter; rated for engines with a fuel pump. It appears that the filter recommended for my engine is the 394358S filter which is 75 Microns. This filter is white and smaller (I think). Wouldn't the 394358S be MORE restrictive of fuel flow because it is filtering smaller particles? More restrictive is not what I want.
I have no idea what filter came with my engine and is still on it. It is much larger than the 691035; mostly clear plastic but one end is a flat plate of metal. The element appears to be paper of some sort. I think I have seen this type of fuel filter in very old cars. The only marking I see says it was made in Taiwan. I should probably just replace that filter with the 691035 that I already have.
Chartman.
PS I don't think you'll be able to see through that open fuel valve.

jp1961 said:

Hmmm,,,the "significant slope" statement would lead me to suspect debris in the tank sloshing around in the tank and occasionally blocking the fuel supply.

Regards

Jeff

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Hi JP. Thank you for weighing in!
I really cleaned that tank out well and I blew it out with compressed air. I pulled it right out of the tractor to work on it.
I agree that the symptoms suggest debris in the tank, but my troubleshooting suggests otherwise.
Chartman

Boobala said:

I have the same problem with my mower at times, only when mowing the slopes in my yard, I'm sure it's the carburetor float so I just get on the other side of the slope for a few seconds, now I mow up & down the slopes sideways up one and like a "snake" to the other side ( like mowing an "S" pattern ) as far as the filter goes it's normal for the amount of fuel in it to change (unless it's blocked of course) it seems your issue is on the slope, as you stated doing front yard, it was functioning OK I have the same engine 31c707 series but a 17.5 HP.

I completed the front yard with no problems and went straight on to the back without stopping.
About half way through, the same fuel starvation problem began. The engine sputtered every time the slope of the terrain tilted the fuel away from the engine.

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Hi Boobala, (...Boobala?)
Thanks for taking the time to weigh in on my problem.
I'm sorry you're having the same problem with your engine. I might try your "snake" mowing approach to help maintain fuel flow; but I would much rather see if I can fix the problem.
You say, "I'm sure it's the carburetor float..." but do you mean that this float is not working properly, or it is just what must be expected when mowing on a sloped lawn? Have you tried to "fix" the float?
This is enough of a problem for me that I would try to repair or replace the float to see if it fixes the problem. I will let you know how things turn out.
Chartman

The 394358S is 75 microns which it will not restrict fuel flow.... It's a smaller filter in size but has the bigger mesh inside of it.....

I opened a shut off valve and looked at it.... It is a bypass valve. That means the fuel goes around the center instead of straight thru.....

Hence the clogging sometimes.... Oh BTW you can't feel the flapping inside of the fuel lines... No actual way to check that in a normal garage without special tools...........

Plus Tard Mon Ami ~!~!

Ok I got to haul ***** out a here and go do my Thursday nite radio show with Todd on KBON 101.1 FM

If anyone wants to listen go to KBON.com and on the homepage click on listen live or listen now.... It's free........

Plus Tard Mes Amies...........

This afternoon I decided to get back to the tractor and see what I could do.
With a needle nosed pliers I was able to remove the solenoid from the bottom of the carb cup. This also removed the cup. I decided I would leave the solenoid intact (in case I change my mind about removing it) and just replace it with a short machine screw. I had trouble figuring out the size, but it appears to be a metric 8 mm with 1.0 thread pitch. (Possibly 5/16 with 24 thread pitch?.) I had to cut down a longer cap screw. I had some trouble screwing it in more than a turn or two. Could this be a tapered thread? I ended up using a couple of washers to take up the space; I'm not proud of this job, but it seems to work. I saw no problems with the float and needle valve, but I did not take these off of the carburetor.
Based on the advice I received here, I decided to replace my unknown fuel filter with the 691035 filter, even though it was rated for engines with a fuel pump. I'm having a hard time imagining that the rubber hoses may be collapsing, but I did replace two short hoses; between the shutoff valve and filter, and between the filter and carb. I had the fuel line and the new hose might be a tighter fit; no vacuum leakage.
I decided to leave the fuel level of the tank where it was when I had the trouble last week and to mow just the back yard, which is most pitched.
The engine started immediately, as usual, and I was able to mow for about 10 - 15 minutes without problem, but then the same old symptoms recurred.
My lawn is level near the house, then sloped down hill for about 30 ft, then level again.
I tend to mow around the entire perimeter of the lawn and slowly spiral in toward the center.
The problems began when the engine was running hot, but also when I reached the point in the job where I was riding for long stretches in the pitched part of the lawn.
The sputtering began near the end of a stretch where the fuel tank was pitched away from the carburetor. When I reached the level part of the lawn, the engine typically recovered.
I quickly switched to a strategy similar to what Boobala recommended, using a serpentine mowing pattern, trying to minimize the time that the tractor was tilted in a problematic direction.
Things got worse as time went on and the level of gas in the tank got lower. I finished, ...but just barely. The fuel tank was perhaps a shade below half full.

So, this is looking more and more to me like a functional condition of this engine and tractor, rather than the failure of some particular part or system.
I think it will work fine if I keep the fuel tank VERY full, or mow only on level lawns.
There was no response to my inquiry about retrofitting a fuel pump to this engine, so I am guess that that is not a viable option.
I appreciate all of the responses and suggestions I have received to my inquiry.
It was very helpful and reassuring that I had not overlooked something simple.
Chartman

Fuel pumps are easy to fit but you will need a crankcase pressure take off point.
Easiest place is to fit a nipple to the rocker cover which saves having to drill a hole in the block.
Check the Briggs part list for your engine and see if there is a blanking off plug listed.
Some engines are drilled for fuel pumps even if the pump is not fitted while other will just have a boss cast in ready for drilling.
Drilling it will require splitting the cases to remove the swarf so drilling the rocker cover is a better choice.
From memory Vanguard cast alloy rocker covers will bolt directly onto your engine, but those more familiar with these engines than me will need to verify that.
If so get one of them and be careful where you make the hole so the nipple does not foul on the rockers.
Nipples come both threaded & plain so get a threaded one thus you will only need a thin lock nut inside to fix it in position.