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John Deere 318 B43G Surging and Other Very Strange Behavior

882 Views 7 Replies 5 Participants Last post by  Yooper3039
Hi everyone, this is my first post here as I have just recently purchased an '85 JD 318. When it's running the way it should, it really runs great. But the problem is that it seems to want to surge after a short while of running. The carb is clean, the air intake manifold was very recently resealed, the carb gets plenty of fuel (maybe too much?) and there is spark. I've run into a couple issues with the points and had to replace the unit. I've tested the ignition coil with a multimeter and it stays within spec hot and cold. Fuel lines are all brand new and tank is freshly cleaned. All new filters as well.

Here are a couple of the really weird behaviors I've noticed: the engine runs rich even with the carb set to run as lean as possible. Also, I spent some time messing with the point gap and found that if the engine was surging set to the standard .16, it would stop surging completely if I set the point gap way too high like .3 for example. Audibly you can tell the engine is running rough when the points are at .3 but it doesnt surge at all. Maybe there is an obvious reason for that, but I'm very new to this and not much of an engine guy.

It's worth mentioning that compression is at 60-65 PSI for both sides (I know this is on the low end according to official specs but is it enough to cause this weird behavior?). Not sure what else to add off the top of my head but if you need/want any more info I'm happy to answer.

Thanks in advance for any help in diagnosing this weird behavior
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My 318 has a surge on occasion, I found if I blow carb cleaner into the hole you see looking down into the carb, it will blow small black chunks out the top vent, and then run great. I assume my fuel line is deteriorating.
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