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18hp Briggs Problems


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#1 gsl54 OFFLINE  

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Posted June 25, 2012 - 11:25 AM

At idle the engine seems to run fine, but when I engage the mower deck it starts to sputter and backfire. Most of the time it eventualy smooths out till I get into thick or tall grass then it starts to backfire. I have cleaned and rebuilt the carb. I have been told it could be the govenor. It is on a 12 year old AYP/Rally. The motor is a 18hp apposed Twin 2
Model #422707-1211-01Any suggestions would be appreciated. Thanks Garry

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#2 maxedout OFFLINE  

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Posted June 25, 2012 - 12:11 PM

I have a Kohler engine that is similar, I've rebuilt the carb, new plug, checked compression, new fuel pump, new line, new filers, cleaned engine, re-adjusted the Governor, replaced all the gaskets on the fuel pump, and carb and mine runs fine at low idle and it runs fine with the deck engaged or under load but high run it seems to run ruff at times and run smooth at times...

I've been told the governor was bad and all sorts of other things. I've even been told it was the valve seats. Which all these things could cause a problem just not sure if it's my problem.

#3 dave8338 OFFLINE  

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Posted June 25, 2012 - 12:43 PM

It sure sounds either governer or ignition related, to me. The spring that connects the governer lever to the carb should be in the middle of the five holes in the lever. The further out on the lever the spring is located, the longer delay there will be in the governer. Likewise the closer in towards the governer shaft the spring is located, the quicker the response.

As for the ignition, have you changed out the plugs and gapped them correctly?

#4 Kurtee OFFLINE  

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Posted June 25, 2012 - 12:53 PM

I had a Snapper rear engine rider years ago that would give fits sometimes. It proved to be in the safety switches. I disconnected them and it worked great. Please bear in mind that I am not advocating disconnecting safety switches in general, but to bypass or disable for testing purposes only. The Snapper had switches that would short out the ignition and kill the machine. These switches would cause sputtering and other engine issues intil disconnected. Also my Exmark sat in the rain once and the machine did weird stuff. After drying out it is fine again. The Exmark is not allowed to sit in the rain anymore. Good Luck; KURT

#5 JDBrian OFFLINE  

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Posted June 25, 2012 - 02:22 PM

I have a Kohler engine that is similar, I've rebuilt the carb, new plug, checked compression, new fuel pump, new line, new filers, cleaned engine, re-adjusted the Governor, replaced all the gaskets on the fuel pump, and carb and mine runs fine at low idle and it runs fine with the deck engaged or under load but high run it seems to run ruff at times and run smooth at times...

I've been told the governor was bad and all sorts of other things. I've even been told it was the valve seats. Which all these things could cause a problem just not sure if it's my problem.


Is the throttle bushing worn on your carb. If it is it will cause it to run a bit off and sputter occasionally. I'd check all the other usual suspects like head gaskets, ignition, etc.
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#6 maxedout OFFLINE  

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Posted June 25, 2012 - 03:02 PM

Is the throttle bushing worn on your carb. If it is it will cause it to run a bit off and sputter occasionally. I'd check all the other usual suspects like head gaskets, ignition, etc.


No, all the bushings on my carburetor have been replaced both on the throttle and choke. Head gasket is good and the points, condenser and coil have now been replaced on mine. Everything I can imagine to check has been checked over and over, it mows fine and runs ok but the sputter now and then is annoying more than anything.

I had a Snapper rear engine rider years ago that would give fits sometimes. It proved to be in the safety switches. I disconnected them and it worked great. Please bear in mind that I am not advocating disconnecting safety switches in general, but to bypass or disable for testing purposes only. The Snapper had switches that would short out the ignition and kill the machine. These switches would cause sputtering and other engine issues intil disconnected. Also my Exmark sat in the rain once and the machine did weird stuff. After drying out it is fine again. The Exmark is not allowed to sit in the rain anymore. Good Luck; KURT



I have seen several safety switches cause some really strange things to happen with an engine. They can make one run ruff too because the engine isn't getting the correct voltage on all the switches it thinks its being told to shut off. That may not be the correct thing to say but it was the easiest thing to explain it for me! LOL!

Those switches after they get some years and age on them are about as worthless as tits on a bore hog. I once thought I had a bad coil and replaced it two times before one of my friends found a bad switch. Keep in mind a switch might check good with a meter but it's not always good. It can get crud inside and and when you are driving around it will either make the switch open a degree or close some and then the firing is messed up.

Those things are so annoying and Like mentioned for testing purposes to unhook might be fine but in the end you the owner should make your own minds up and do what you yourselves think is right concerning those switches.

#7 JDBrian OFFLINE  

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Posted June 25, 2012 - 05:04 PM

Also check for leaky head gaskets. When the engine heats up they can cause some strange problems. The other thing that comes to mind is to make sure that the cooling fins and screens are clean so the engine is running at normal temps. If it is running hot you can get fuel vaporization. My Kohler K321 does the sputtering thing as well but it has a worn throttle bushing and also a cracked block. Hopefully you don't have that problem.

#8 MH81 ONLINE  

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Posted June 25, 2012 - 10:43 PM

Does this engine have a fuel shut off solenoid in the carb? It may be rattling if worn, and causing fuel issues. Several members have fought with them over different symptoms. Just something else to try if you've exhausted the bulk of the regular issues.

Next thought. Are the mufflers OEM? If not, I'd jump right on the valve seat bandwagon. The aftermarket muffler(s) can cause the exhaust valve seat to cool quickly vs. the rest of the block. Repeat, repeat, repeat and eventually they start to loosen up.




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