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Discussion Starter #1
Hello Everyone,

New member and first time poster.

I have a 1985 JD 318 with the B43 Onan. Over the past two years it started stalling when hot. It's gotten worse and now will only run for about 5 minutes then stall. It will immediately start back up and stall again. Not related to the PTO (or any interlocks). The engine runs great, like a sewing machine!

I'm a bit stumped. Here is what I have done so far (no joy):

1) Cleaned the carb
2) Changed the plugs
3) Checked the resistance on both coil windings (both within spec.)
4) Replaced the condenser
5) Checked fuel flow (good, even at stall)

Could the coil be going bad even if it's within spec? I did not change the points but have a new set ready to install. Ideas? Thanks
 

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Is the engine truly HOT when it stalls, or just coming up to operating temperature? Because if it is truly HOT then what is happening is the fuel is being boiled out of the carb before it can be mixed with air. That means pulling the engine and removing the oil pan and checking the pan for metal (bearings), sludge buildup or buildup on the oil pickup. If it it dying just coming up to operating temp, then i would hazard a either a bad coil (dielectric breakdown, winding), condensor breakdown (should be on the negative side of coil in a standard points Onan), spark plug wires, spark plugs.
 

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Discussion Starter #3
Is the engine truly HOT when it stalls, or just coming up to operating temperature? Because if it is truly HOT then what is happening is the fuel is being boiled out of the carb before it can be mixed with air. That means pulling the engine and removing the oil pan and checking the pan for metal (bearings), sludge buildup or buildup on the oil pickup. If it it dying just coming up to operating temp, then i would hazard a either a bad coil (dielectric breakdown, winding), condensor breakdown (should be on the negative side of coil in a standard points Onan), spark plug wires, spark plugs.
Hello bloodrunsgreen,

Thanks for your prompt reply. For clarification I'm defining hot as coming up to temperature or at operating temperature and not overheating. During diagnostics I've been running with the air cleaner pulled and the carb exposed. No evidence of vaporizing fuel. It's not overheating. This engine is well maintained and very clean.

I'm thinking ignition problem which is why I'd ask if anyone had seen this kind of issue when a coil checks okay. I've already replaced the condenser and plugs. I suppose it could be a plug wire, that would be a cheap fix. Anybody have this issue with a plug wire? Thanks again.
 

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Check the plug wires, especially in the boots, look at where the wire meets the crimp. Use a VOM or DVOM check the resistance it should be zero if they are straight plug wires and not the resistive type. Make sure the connector is tight on the plug and tight in the coil, check the towers on the coil for corrosion.
 

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When my '85 318 died when hot, both times it was the condenser but you have eliminated that problem.

Do the cheap stuff first. Does it stay in the non-working state long enough to check for spark/no spark condition? When it dies will it start with a jumper from battery to positive coil terminal? I'm guessing you have done that to eliminate the safety switches but asking anyway. Are the cooling fins behind the engine side shields clean, long shot? Plug wires are cheap, around $15, replace them. An ignition switch is around $25, if nothing else replacing it is good preventative maintenance. The coil should be OK, maybe not, but a coil is around $100. When it dies do you have dash lights? If not, do you still have the old glass fuses? They should be replaced on sight for preventative maintenance too. If no dash lights also check circuit breaker, only $25.

Some ideas I had. Do things one at a time so you know what fixed the problem. The problem could be related to vibration and not heat.
 
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