JD318 backfires

be182 · Jul 13, 2014

My 1985 JD tractor started backfiring today. It's hot out -95 degrees. Don't know if that has anything to do.
Also last 2 days hard to start. Don't know where to start troubleshooting....
Last year had the entire tractor gone over - new coil, entire new fuel line, filters, gas tank down and cleaned, new mesh filters, carb rebuilt.
Thanks for any help.

bruceatlam · Jul 13, 2014

Does that carb have a fuel solenoid on it??? If it does, that would be a good place to start.

4020deereboy · Jul 13, 2014

does it have the P series engine? Also have had the electric pto clutch be bad start to overdraw amps a cause the engine to cutout and backfire. shutting off the pto when it starts backfireing is a simple check if it stops clucth going bad.

be182 · Jul 13, 2014

I don't know if P series - it is Onan engine, hydrostatic. Shutting off the mower deck does not stop the backfire. I checked plugs, are ok, wires ok. I don't know how to tell if there is a fuel solenoid. ... I did put some choke-carb cleaner in. After I looked at everything, and put all back together, mowed almost 3 acres before it started to backfire again. thanks again for any help.

mfreund · Jul 13, 2014

Take the battery out and have it load tested. Also check the air gap to the clutch. After those two check ok check coils with a ohm meter.

4020deereboy · Jul 13, 2014

P series was performer series engines with electronic ignition. Pre P series engines had points and comd. had trouble in past with point plunger wearing off effecting gap. Their was at a time in the day the field installed what was called a fuel dashpot. It was in laymans terms a antidiesel solenoid install on the load jet to shut fuel off.

DJ54 · Jul 14, 2014

I may be reaching here, but if this is the first time it has done it, and only when the temps were high, it may be a possibility an exhaust valve may be hanging open a bit.

Some may scoff, but get the smallest bottle of Marvel Mystery Oil, and add prescribed amounts to crankcase & fuel. Run it, but don't work it hard for a bit, and let it get things lubed up.

I realize this was built to run on unleaded fuel, but all of my older engines that weren't, I keep them dosed with MMO. I did have problems with exhaust valves sticking when air temps were high, and working them hard, until I tried this, and no problems since.