John Deere 318 Runs Rough

bml19 · Jul 9, 2014

I have a 1994 John Deere 318 with an Onan engine. The tractor has begun to start hard and I noticed it was initially running a little rough before eventually running smooth. This problem has continued to get worse. The past few times I have used it, it takes longer and longer to smooth out. I have run a couple tanks of gas through it since this problem has started and have changed the plugs. I have blown out the air filter and it looks fine but I do plan to replace this and the fuel filter. I doubt this will solve the problem, as the motor gets hot it seems to run better. Any other possible solutions would be appreciated.
Thanks, Bill

jd_adict · Jul 9, 2014

Hey bill, I had the same kind of problem with my
318, turned out it was the carbon core spark plug
wires. they just seemed to disintagrate inside .
My wife needed it on demand one weekend when it
wasnt running and I ended up makeing new copper core
wires because JD was closed. It runs better that
new. I think them bad plug wires were acting up
for a while. You gatta remember, it is getting
old. Hope this helps.

MikeJM · Jul 9, 2014

Another thing to look at is the intake manifold gaskets, we ended up having a similar problem with ours and that's what it turned out to be. Whiles its running rough spray around the gaskets with carb clean to see if it smooths out and you'll get your answer pretty quickly.

Bob · Jul 9, 2014

Mike gave you good advice about the intake.

Also, those carburetors are known to be bad for getting dirty or gummed up in the lower section.

Might as well take the intake of and examine it closely, then open up the carb and thoroughly flush out all passages with sprat carb cleaner followed by compressed air.

KIP in MX · Jul 9, 2014

I have a similar problem with mine sometimes except it starts and runs fine then starts missing when hot at mid throttle. You might want to check the points and gap properly since the gap sets the spark timing. That usually cures my engine.

MikeJM · Jul 9, 2014

Bob just reminded me of something, I believe it was on the Onan carb, but I could be wrong, I have slept since then.

A little welch plug fell out of the carb and was causing the rough running, but I can't remember if it was the Onan or not. Its been a while and its not the only twin cylinder we have to work on.

Aussie Ken · Jul 13, 2014

I worked on a 425 with 2 cylinder Kawasaki carbureted engine. would start fine but miss at half and full throttle. I used pure acetylene around the intake manifold gaskets and it smoothed out immediately. turned out a section of intake manifold gasket had dried out and disappeared - replaced gasket and it ran great!!!

kb9r · Jul 14, 2014

Hi Bill,
I had a problem like yours and it turned out to be the gasket and mating surfaces between the intake manifold and the block. I found it by spraying some WD-40 in those areas. When I hit the leak, the engine instantly ran better. (careful about fire hazard). So I changed gaskets and surfaced the manifold with a flat surface and some emery paper as I remember.
Hope this helps Bill,

Joe

bml19 · Jul 24, 2014

jd_adict, I think you have gotten me closer to solving this problem. While it was running, I pulled the plug wire on the left side, it immediately started to stall. I did the same on the right side and it continued running rough. It was only running on one cylinder. I replaced the spark plug wires and it is a lot better but lacks power when I try to mow. After about 5 minutes when it got hot, full power seems to return and it mowed like it used to. I believe the wires were bad but I also believe the coil may be weak. If I pull the left side with the new wires it will stall, if I pull the right side it just goes back to running rough. Does this sound right? Thanks Bill

bml19 · Jul 24, 2014

I believe jd_adict may be on to the solution. While it was running, I pulled the spark plug wire for the left side, the tractor immediatley began to stall before I put it back on. I pulled the right side and it continued to run rough. It was only running on 1 cylinder. I put new wires on it and it runs much better, I thought I had it until I tried to mow. It still lacks power. After 5 minutes when it gets hot, it started mowing like it used to. While it was running, I pulled the left side again, it stalls out. I pull the right side and it goes back to running very rough. I know the wires were causing a problem but I believe the coil may also be weak, does this make sense? Thanks Bill

Bob · Jul 24, 2014

DON'T pull plug wires! The HV will find someplace to go/seek ground, and possibly damage the coil!

Since this is a "waste spark" system, there is NO ground connection at all, to the coil secondary. For one plug to fire, the end of the secondary winding disconnected from the opposite plug HAS to "find" ground!

If you want to check for misfire, remove the sparkplug boots and GROUND the plugs, one at a time.

HINT: Silicone spray lube makes removing/re-installing the boots a LOT easier!

John Deere 318 Runs Rough

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