Did a rebuild on a 1999 sportsman 500. New carb kit, new stator, bored out and all new gaskets etc. Went to start it today and it started up nice and purred, then it idled down and died. Lots of smoke, I think it's the oil burning off the cylinder walls though. Went to start it again, and gas was spitting out the carb and it backfired and the motor just hits a dead stop after the starter stops. It goes like "crank crank crank" "fires" "dies" "motor clunks and hits a dead stop" I'm guessing it's either a carb or timing problem. Any help?

 

Do a compression check,should be between 55-90 psi on average because of the compression release on the cam. Plus was the cam checked/replaced? This was in the year model range for soft cams that could eat up exhaust lobes.If you installed a carb kit and it's set properly,but spitting gas out of the carb,would check the cam and cam timing. Hitting a "dead" stop could because of timing or even can be because of a bad rod bearing on the crank and trying to lock up.

 

I'm going to check the can for sure. It looked fine when I re assembled the motor but you never know. Forgot to mention the thing is smoking real bad. Not coolant in the cylinder, I'm pretty sure it's oil. Because I had some black oil come out the exhaust. I wonder if that oil is just enough to effect how the engine is running. It might be killing the spark on the plug. Maybe I just have to run it some more and burn off the oil I put in the cylinder and valves.

 

Could take a little time for the rings to seat. If it continues oil smoking after a couple hrs could be a broken oil ring or cylinder possibly could have been bored too large. Piston to cylinder clearance specs by the manual are tight. .0006 - .0018 Service limit shows .0024 max clearance.

 

Pretty sure it's the cam. Got it running again today and it seems like there's no power when you rev it. Which is a common sign of exhaust lobe warn down. Also I think the reason the gas is spitting back out is from too much back pressure because the valve isn't opening. So my bet is its the cam.

 

Common problem. If it looks like this it's worn out.Bad Cam Pic - ATVConnection.com ATV Enthusiast Community
Plenty of cam kits on ebay. Always replace the exhaust rocker arm also.http://www.ebay.com/itm/NEW-ROCKER-ARM-CAMSHAFT-POLARIS-MAGNUM-425-2x4-4x4-6x6-1995-1996-1997-1998-CAM-/360496402521?hash=item53ef429059&vxp=mtr

 

Well I the cam out, and there is hardly a scratch on it! I guess ill have to check the timing and carb next. I thought it would have been the cam for sure.

https://drive.google.com/file/d/0ByQ...ew?usp=sharing
https://drive.google.com/file/d/0ByQ...ew?usp=sharing
https://drive.google.com/file/d/0ByQ...ew?usp=sharing
https://drive.google.com/file/d/0ByQ...ew?usp=sharing

 

Look at the pad on the exhaust rocker arm! Shouldn't be scored like this.. Look again at the exhaust lobe and mic it against the two intake lobes..Plus the detent ball could be screwed up in the cam causing the scoring and causing it to run bad.Check the decompression release lever and spring also.

 

I know when my cam was bad the 2 times i had to replace it, it would idle and idle nice....just would not rev up for crap. But it did idle okay and i had almost no exhast left.

Also there is 3 lobes!!! Make sure your looking at the one in the middle not just the end 2, i know i had a few guys look at my cam and say whats wrong, thinking that the 2 lobes where all there was suppose to be.

 

I dont know if the cam is my problem, I took measurements and my cam is out by a few tenths of a millimetre. The exhaust lobe is supposed to be 32.726-32.826 and mine is 32.4. The detent ball is going up and down just fine when the decompression lever turns. Im not sure, that little bit off the cam shouldn't make that big of a problem.