90 marathon loses power after warms up

dan161

First off I'm relatively new to the cart world and love reading post and learning. I recently purchased a 1990 marathon with the pg3 motor in it. It has new carb, new fuel pump with strong flow, newer rebuild on top end, 120psi cold and 110psi hot compression, high torque spring in driven clutch, 4in lift kit with 22X11 inch tires, new belt and governor is attached but tightened up pretty tight. The problem is it runs good when its cold but after it warms up (3-4 minutes) it really starts bogging down like somebody dropped the anchor. After I put the new driven high torque spring in it helped alot, but it still has the same problem.

I am in the process of getting the muffler barbecued, but I am looking for any other ideas what may be causing this to happen cause I don't think the muffler was that bad. The clutches seem to be operating correctly with normal wear and tear on the driven clutch at least. Haven't had the drive clutch off but it seems to be operating fine. Its really noticable when under power like going up a hill or something. Put on jackstands and it runs with no problems. I am at wits end here with this so any ideas you have would be welcomed with an open mind. Thank you kindly.

BGW

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racin161

Dan try running it in reverse and see if it does the same. Reason possible crank seals sometimes it will run great in reverse but not forward. The problem is you can't see the seal under the flywheel to inspect it but you may look at the drive clutch side and look for signs of oil or a piece of rubber looking at you.

LOU

dan161

Thanks Lou. I will give this a try. There is alot of oily residue down around bottom of motor. I don't understand how this would make it slow down after it gets hot, but I'm willing to try anything.

WJ ezgo

..also perhaps the coil is going bad. As part of a tune-up, I always replace ignition coils particularly for vintage machines. When they heat-up, tiny cracks that developed over time open-up around the housing and then cause an intermintent spark/no spark at all. Then when it cools it starts/runs fine.

dan161

Thanks WJ. I will check. It doesn't act like its missing at all though. Runs smooth, just doesn't have power.

Dave Box

There will always be unburnt oil residue in the exhaust and this coats the baffles in the muffler eventually almost blocking them. When the muffler gets hot the residue expands and completely blocks the muffler preventing the engine from breathing. You describe the exact symptoms of a muffler that needs an hour on a hot campfire. However if you have not yet removed the muffler then undo the bolts between the exhaust and the muffler to create a 1/2 inch gap. See if this improves the performance.

Dave

dan161

I burnt out the muffler last night, but haven't gotten it back on yet to see how it works. I did drive it a bit without the muffler on it and it seemed pretty good but then again the engine wasn't warmed up yet. The oily residue I was talking about is down around the bottom outside of the motor. I have sprayed carb cleaner down in around the bottom part of motor when its running and it doesn't change anything.