Mowing John Deere 318 Stalling Problem

[MicMacLenn]

My John Deere 318 with original onan has recently begun stalling after 10 to 15 minutes of mowing and will not restart until it cools off. It isn't my seat switch as I just replaced it. The PTO switch seems to be working OK and I just replaced the spark plugs too.

Could it be vapor lock?

Any advice would be appreciated.

Could it be a bad Coil?

 

[glc24]

Hello and :welcome: to TBN

I'm thinking it is your coil. The symptoms you mention are usually what happens from a weak coil.

Greg

 

[MicMacLenn]

Thanks - it was my coil, I replaced it and my JD is running great again!

 

[dugman]

My 318 is running rough (stalling, backfiring) after 15-20 minutes (longer when temp is cooler) of mowing. I have read many threads on this issue and have done the following over the past few months:
-replaced the coil
-jumpered around the interlocks to eliminate them as the problem source (Battery +12V directly to ignition module)
-replaced the carb, fuel filter and fuel lines
-cleaned the gas tank and tank pickup filter
-compression good both cold and hot
-changed plugs and wires
-changed condenser

The onan P218G engine was rebuilt about 3 years ago and only has 20 hours or so on it. It has been running rough since the rebuild. I have not checked the valve clearances, ignition module or intake manifold seal. I did check the timing and it looks reasonable but jumps around when it gets into the running rough/backfiring phase. Cooling the engine down helps alleviate the roughness immediately. The engine cooling fins, shrouds and belly screen are all clean. The running rough issue can be made worse by tilting or rocking the tractor or driving uphill. It is much worse under load (mower deck) It will clear up and run fine if you disengage the PTO.

I'm pretty much ready to throw in the towel and hoping that someone may have an additional idea or two.
Thanks!!

 

[Henri88]

The tilting or rocking should point toward the float of the carburetor, but you have already change that. Sounds like it starving gas but again you look into that also. The only thing you have not look into is your fuel pump if equip. Not sure about these model, but there could be a mechanical pump.

 

[dugman]

That is a possibility. I did checked the level of fuel in the filter while it runs poorly and there seems to be plenty of fuel. It does smell like its running rich when this happens. K7LN has suggested checking/eliminating the governor as a culprit. Hopefully I'll get a chance this weekend to troubleshoot this! Thanks for the feedback!

 

[dugman]

Update:

The problem was the ignition module located behind the flywheel. The wrong insulator was installed which allowed the module to get too hot (almost directly in contact with the crankcase) causing it to fail. Replaced and the 318 now runs perfectly!
Thanks for all your suggestions!