I have bought a 1996 Sportsman 500 and am having trouble getting it to run right. It basically runs ok in the low rev range but will not rev properly over 1/2 to 3/4 throttle. My local Poaris dealer did all the obvious checks and then diagnosed the problem to be a worn camshaft, which he duly replaced. The bike is still with the dealer as although it is better, it still isn't right. Thery have told me that it runs fine with the air filter disconnected but bogs down with it connected. The air filter is new and clean. They have also tried a different carburretor but this did not solve the problem.
Can anyone please help with this baffling problem so that I can get out and enjoy my Polaris.
Thanking you in advance.

 

If it has a new cam it could be any thing from a plugged gas vent line to a stopped up muffler.
Even a bad rev limiter or clutch can do it too.

 

Possible to be a tooth off when they timed it

 

Thanks for your reply. Unfortunately the delaer has had no luck in solving the problem and has no resorted to putting all the original parts back on, including the cam, and starting from scratch again.
If the air box is completely removed the bike runs fine. If the air box is re-introduced to the end of the carb the engine starts popping and banging and generally running very badly. Obviously this is something to do with air flow but what is causing it is a mystery.

 

Well these are always just a guess ………….here we go.

If your machine runs well with the air box off, then I would think it’s not a cam problem now ………could be but unlikely.
More likely a plumbing problem with the carburetor, there is a plunger that needs a certain amount of vacuum to function this should be checked along with float adjustment and generally the whole intake system.

Try and pull the choke when you have it running and see if it improves or gets worse.

I do like the fact that the dealer said to replace everything and start over!
As long as he’s not charging you for it, it is a way of logically breaking down the problem.
.

 

When your dealer pulled the valve cover and looked at your cam it was obvious if it was worn out or not.

He had no reason to replace it if it was not worn out.

I think the people working on your machine have no idea what they are doing.

 

I'm beginning to think that as well! The dealer said that the cam does look worn and although the new one has improved things its not cured the problem. As you say, it's either worn or it isn't. They are Polaris dealers and have been for several years so they should know what they're up to!

 

I would tend to agree with Zbart. My 97 did this for a year before I found the problem. I know he replaced the carb but I would look at the bladder in the carb as the cause it will look fine but it will have a small leak in the center of it, at least mine did. Once this was replaced it worked as good as if it were a new machine Hope this helps you out!!!

 

its got to be the carb if he pulled the air filter off and it ran good. its the other way around, when you pull it off it should run like crap. i would say its got to be an air isusse for sure. maybe its not getting the right vacume pressure.