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1994 Polaris 400L rough running

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I have a problem with my 1994 Polaris 400l, it has been running bad for a while, the last time we took it out we had to change the plugs twice as they blackend/oiled up and the bike started running rough, i've stripped down the carb and cleaned it all out, i've checked the oil pump mix ratio, the reeds are seated correctly, the air cleaner is clean.

the idle screw is wound all the way in and i still had to adjust the throttle cable at the control to get the bike to idle. low end is lumpy and the bike will not pull uphill, on a flat the bike will run smother once the bike gets moving but there's not the speed there used to be.

I also checked the bottom of the piston and there appears to be no damage there, the engine sounds ok when it idles, oh and i also checked the exhaust and that appears to be ok.

One more thing, the bike was put on it's side around 3 months ago and when it was restarted i had to turn up the idle screw so it would idle. Any advise would be great.


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It sounds like oil is leaking into the crankcase, most likely crank seals, but it could be the center case gasket. I would start with the crank seals because they are cheap and easier. If you end up having to split the cases, you might want to change the crank bearings as well, since you are already in there.

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That would explain it but the bike is a 2 stroke, it has a counterballancer and i read there is a sump in the crankcase, is that what your talking about?

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Today i unhooked the oil pump and put premix in the tank, also checked the counterbalancer oil level and it's not low, also the new plug was wet with oil, running it with premix gas improved the operation slightly.

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First thing I would do from that point is keep pre-mixing your fuel, and properly block off the oil injection. Since you said running pre-mix improved things slightly you may just need to burn off the excess oil that may have accumulated in your crankcase. The oil injection system may have been putting to much oil to the motor. If that doesn't work, then you may be getting the oil from the counterballancer housing. Normally on a two stroke motor there will be oil on one side of the crank that is held out of the crankcase by a seal that goes on the outside of the crank bearing. Your motor looks to be a bit different than what I am used to seeing but there is definately oil on the outdrive side of your crank outside of the crankcase. This oil is for the counterballancer and the gears that run it, one on the crankshaft and one on the counterballancer. I also noticed that the oil pump you were talking about seems to be mounted in this area as well. I would guess that the pump circulates oil between the counterballancer and the gearbox which is separate from the rest of the motor. From what I can tell, you could be leaking oil from the counterballancer into the crankcase because the case center gasket is leaking or because the right hand side crank seal is leaking. It looks to me like you will have to remove the recoil starter, flywheel, stator, and the cover behind the stator to get to that seal. To get to every thing else you would have to split the case halves. The other crank seal even looks like it goes on the inside of the case.

Edited by DirtDemon

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Ran like a dream today, no bogging out, able to climb hills, just have to strip and clean carb one more time but looks like the problem may of been the oil pump, i'll let you know as soon as i do.

It died today after running good for about 20 miles, would not start and then when it did start it sounded like it was starving for fuel, plug was pretty clean and would only start on the choke, took the carb off and cleaned out again, started it up and on full throttle it would only run for a few seconds and it took full throttle to idle, any other ideas?

Many thanks.

Edited by Miles_Togo

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