ez go marathon 4 stroke wont rev up

golfnut@199

Hello, I have a ez go marathon that wont run past half throttle.. It also backfires through the carb.. I have changed the oil, replace carb with new one from ez go.. I have replace all the filters, adjusted valves many times.. removed the muffler and checked for blockage.. bypass all micro switches.. replace plugs, and fuel pump.. It has good fire and will run but not very well.. When its running you can remove either spark plug wire and it will quit backfiring but still runs poorly.. It was completly overhauled by ez go dealer about 5 years ago. And it has over 120 psi compresson on each cylinder.. I'm bout outta tricks.. Any help would be greatly appreciated..

BGW

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kyerik

Does it run better when you choke it a little bit? If so, check for an intake manifold leak.

Is the ignition timing adjustable on the 4 strokes? (it is adjustable on my 91 2 stroke). If so, try advancing the spark timing a bit. I had to remove my flywheel, but the pulser was mounted to a plate with slotted holes and I just needed to turn the pulser opposite the direction of crank rotation in order to advance the timing. My engine would not rev up well at all before and now it revs nicely. (I noticed that it would rev in reverse- that is what told me that it was a timing issue).

If your timing is not adjustable- you might double check that your flywheel key isn't sheared off- that would affect timing (assuming that something on the flywheel triggers the pulser pickup).

You might also use an inductive timing light and make sure that the spark going to both plugs is regular and even (shine the strobe light at the clutch pulley). Perhaps your coil is going bad and the spark is erratic.

golfnut@199

Choking does not seem to make any difference.. The coil has been replaced with a new one from ez go.. I'm not sure if the timing is adjustable? I will have to research that some more.. Thanks for your help..