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Let me start this off by saying im new here. I work on small engines all the time, though i cant just figure this one out I figure theres probably guys here alot more experienced than me, have a shot at it - i tried to be pretty detailed. :smile:



Been messing with a riding mower my grandmother gave me, its like new but it quit on her and she went and bought another one. Has a briggs 14.5 OHV on it. Originally had the ****ty "nikki" carburetor, i tossed that in favor of a walbro (completely rebuilt) from another running 14.5 that had a knock.


When i got it i found the intake valve not opening was causing no start. No biggie, popped the valve cover, had a broken pushrod. Replaced pushrod, set both valves to .006 gap COLD.


Popped the flywheel cover off and pulled flywheel, key was fine but i replaced it anyway, sanded rust off flywheel and coil, coil gap is fine. New plug, strong blue spark when cranking. Also has fresh oil change of briggs SAE 30 oil.


Go to fire it up, it will turn and turn and not sound like its hitting at all, then itll POP and smoke back through the intake every 5-10 seconds or so while cranking over. This is with choke on, with choke off it just fires over and doesnt change a tone.





Heres whats NOT wrong with it that ive figured out.

Cam is timed correctly (verified correct piston location and valve timing with dial indicator)

Spark is timed correctly

Getting fuel, float not leaking, jetted correctly

Choke linkage and throttle linkage working correctly

All sensors working properly

Motor has plenty of compression, only about 10 hrs on whole mower.




What can it be? Only thing im thinking is there may be something with the valve lash. I may try opening it up to .008 and see if that helps. Ideas? I normally dont have this much trouble, but this damn thing is killing me.

sounds like a valve is hanging open. you should do a cylinder leak down and see if you can here air leaking past a valve. I had a small OHV motor that would not even fire on starting fluid. I did a leak test and intake valve was staying open. I cleaned and lapped the valves and it fired right up.

Hope this helps you,
Rob

I was thinking of that too, Rob. Im gonna try and open the valve lash up some and see how that works and ill report back. My next plan was to pull the head and check the valves, though with a mechanics stethascope and pressurizing the cylinder i cant hear anything leaking.

You may also check the engine model you pulled the carb off of and the new engine model and make sure the walbro carbs are the same that it calls for both engines, just incase they ported it differently.

Check the compression... it will tell you the condition & operation of the valves...
Have you been able to get it to try to start using starting fluid???

:smile:KennyV

Well, i figured out what it was. I reset the valve lash today and still nothing. Decided to pull the flywheel and check the condition of everything once again. What happened is when i replaced the flywheel key the first time i pulled the cover to inspect it, i apparently didnt impact the flywheel on tight enough. So i pull the flywheel cover off today and see that its sheared. I noticed that it was sheared almost 180 out so got my degree wheel and it was sheared about 177 degrees from where it should be, LOL :laughing:

This must be why when i checked to verify it was firing at tdc, it was actually firing at the wrong TDC? Im not quite sure. BUT, i replaced the key, impacted the **** out of the flywheel bolt, and it fired right up and ran with no hiccups. Cut my 2 acre yard with it, then took it over and cut my moms 2 acre yard. Used about 2 gallons of gas through it, runs like a sewing machine now. All this time i thought it was carb trouble caused me to religiously clean the carb but i guess thats a good thing.

Good show! Sometimes starting back at square one is about the only place you can.:thumbsup:

BradButlerNC said:

Let me start this off by saying im new here. I work on small engines all the time, though i cant just figure this one out I figure theres probably guys here alot more experienced than me, have a shot at it - i tried to be pretty detailed. :smile:



Been messing with a riding mower my grandmother gave me, its like new but it quit on her and she went and bought another one. Has a briggs 14.5 OHV on it. Originally had the ****ty "nikki" carburetor, i tossed that in favor of a walbro (completely rebuilt) from another running 14.5 that had a knock.


When i got it i found the intake valve not opening was causing no start. No biggie, popped the valve cover, had a broken pushrod. Replaced pushrod, set both valves to .006 gap COLD.


Popped the flywheel cover off and pulled flywheel, key was fine but i replaced it anyway, sanded rust off flywheel and coil, coil gap is fine. New plug, strong blue spark when cranking. Also has fresh oil change of briggs SAE 30 oil.


Go to fire it up, it will turn and turn and not sound like its hitting at all, then itll POP and smoke back through the intake every 5-10 seconds or so while cranking over. This is with choke on, with choke off it just fires over and doesnt change a tone.





Heres whats NOT wrong with it that ive figured out.

Cam is timed correctly (verified correct piston location and valve timing with dial indicator)

Spark is timed correctly

Getting fuel, float not leaking, jetted correctly

Choke linkage and throttle linkage working correctly

All sensors working properly

Motor has plenty of compression, only about 10 hrs on whole mower.




What can it be? Only thing im thinking is there may be something with the valve lash. I may try opening it up to .008 and see if that helps. Ideas? I normally dont have this much trouble, but this damn thing is killing me.

Click to expand...

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Quote: "When i got it i found the intake valve not opening was causing no start".
Quote: "Popped the flywheel cover off and pulled flywheel".
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I'm having a problem understanding why you pulled the flywheel after you found the push rod problem was causing the no start.

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Quote:" Heres whats NOT wrong with it that ive figured out".

Quote: Spark is timed correctly
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As you discovered the spark wasn't timed correctly. Since you work on engines a lot let me help here in case you need to do a quick check on timing, spark plug spark at atmospheric pressure and a reasonable idea on compression all at one setting within just a few seconds. This would have saved you a lot of time, carb change out and head scratchin.

Next time remove the spark plug, put the plug wire back on the plug and ground the plug to the head with one hand and put your thumb or finger of your other hand securely over the spark plug hole. Have a helper crank the engine. If the timing is correct the plug will spark at the same instant your thumb or finger is blown from the plug hole by compression. So with that simple no cost test you've checked timing (good enough to start and run), spark plug for spark and compression.
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BUT, i replaced the key, impacted the **** out of the flywheel bolt

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I'm surprised you didn't crack the flywheel installing the nut with an impact. It could be and you may never know unless you pull the flywheel and look. It will be cracked in one of the corners of the key way. In small engines there 3 things minimum that I recommend torquing to specifications. Flywheel nut, rod nuts/cap screws and head bolts/cap screws.

Better luck next time.