Well, I got away from the two strokes for a bit. Picked up a clean 96 sportsman 500 that has some running issues. First thought was a bad cam because of the year. The guy who owned it said he had a neighbor who was a self proclaimed mechanic look at it and he said the cam was fine and charged him 200 bucks for looking at it and doing a compression test. He wanted it sold instead of dealing with it so I picked it up. Don't know what the guy charged him for since it was obvious the plug was never pulled to do a compression test and the valve cover was never removed with since it was still sporting the original gasket that was stuck pretty tight. I bought a shindy carb kit, new plug and oil and filter. The carb looks like it was rebuilt recently but u will do that again anyways. Plug was sooty and black, but not oily. Air filter is new. Air box needs 3 studs replaced to make the lid seal properly but it was sealed good with the wingnuts that were still there so I don't think it's an airbox issue. I looked at the cam but it was hard to see the lobes with the gas tank in the way and the valvetrain still bolted in. From what I can see, the cam does look good, or atleasr it does to me, but then again, I'm used to those old noisy two strokes and never did a soft cam 500 before so I don't know what to look for. Aside from the obvious, like rebuilding the carb, unhooking the reverse limiter and the airbox sealing, is there any other issues that would cause bad cam symptoms? It starts and idles fine, and does run good for a bit but once into the throttle it bogs and wants to backfire a bit. How do I get a good look at the cam and also, how do i tell if it needs to be replaced? It pushes the valves down good when I spin the motor over so I don't think the lobes are wore down from what I can tell. If I have to replace the cam, are there any tricks to making that an easy job without too many headaches for a guy who likes his simple two strokes?

Thanks
Mike

 

Pull the black wire from the limiter first and see if that solves the problem.If it doesn't you need to lift the tank cover up enough and the tank to be able to get calipers in there. 1.277 min on the exhaust lobe. You should be able to see if the pad on the exhaust rocket arm is scored also. IF you need to replace the cam,I've got an easy way to do it.

 

Thanks OPT,

Did the carb, air box and limiter. No change. Pulled the cover to look at the cam but everything looks normal. Didn't measure it, but everything looks smooth with no wear. It starts fine, idles, but misses one throttle is applied. Sounds like cam, but not sure.

Thanks
Mike

 

Oh, and another thing, the oil was very dirty like it wasn't changed for quite some time. Don't know if that would attribute cam failure more quickly. It sounds like to me when it's running like the reverse limiter is hitting, bit I eliminated that. I will try and upload a video of it getting revved up.

Thanks
Mike

 

Rocker arm pad has that mark from the decompression ball that all of them have.I'd still pull the round cam cover and make sure the decompression arm works ok and the ball raises and lowers. Check the intake manifold for cracks plus you mentioned the air box broken studs. Use some tape around it to seal it and see if that might help.

 

I had at least 1 of those old *&^%$#@! air-box studs break off on my '97. I'm glad they switched to the spring clip thingies, whatever they're called.

 

Thanks guys,

The ball doesn't move at all. So I assume if the decompression is stuck, it will cause running issues? So it looks like I'm gonna need a cam. How much of a pain is that going to be to change?

Thanks
Mike

 

Here goes,I book marked this awhile back so I never would have to type it again. You can do it this way or by the book,that is tearing it down to the lower crank sprocket which isn't necessary IF you don't move the crank shaft...
https://atvconnection.com/forums/pol...ml#post3212906
Plus here's a recent one with pics if you do want to go by the plated links on the chain.https://atvconnection.com/forums/pol...ml#post3305250