I've got a 98 sportsman 500...this started a while back...it ran perfect but all the sudden it started topping out around 30-35mph, it just lost all power. Then last weekend we had it out, it was running the same but after 3 hours of pulling the brushhog around it wouldn't go more than 5mph or so. It starts very easily and idles perfectly, but even in neutral it won't rev up...i can maybe get 2000rpms out of if, then it falls on it's face. Any ideas? I checked the easy stuff...spark plug looks good, fuel filter looks good and i pulled the carb off and sprayed it out, but it still runs the same. The battery is on it's way out, it won't hold a charge anymore, but the last time we had it out the battery was fine. Any ideas would be greatly appreciated!

 

Check the exhaust lobe on the cam. I have one in my shop with the cam lobe worn off. It happened somewhat frequently on those older 500's.

 

Thanks...i did read some other threads about that...the only thing that didn't seem in line with everyone else is that mine is not backfiring at all where most other people's were. But that's definately the next thing I'll check.

 

After you mentioned that I remembered ONE time and once only I had a machine come in with both intake lobes worn off and the exhaust was fine. Once only. Check them too.

 

Ok...just eyeing up the cam without taking it out, it looks ok. I went through the carb I replaced both jets, the needle valve and the jet needle for good measure and it still runs the same. I think it's gotta be a fuel delivery issue because when i run it to the point where it starts to bog, if I spray some carb cleaner in it, it'll rev right up. Right now I'm running it off of an auxillary fuel tank so I don't think it's a fuel pump or filter problem. Any other ideas? Do I need to take the carb and have it dipped? Oh also for fun...I did move the needle to the highest position, and with the choke fully on it seemed to maybe rev just a little higher.

 

How is the diaphragm in the carb? Any holes, tears or does it rotate on the slide?(some of the newer 500's had a diaphragm that could rotate but the older ones should not) It can cause a similar issue as well.

 

There's nothing obvious that I can see wrong with the diaphragm, no visable holes or tears, is there a way to test it?

 

DOES IT HAVE A REVERSE OVERRIDE BUTTON? IF SO, HOLD IT IN AND SEE IF IT STRAIGHTENS UP.

 

I already tried that, no luck.

 

<div class="FTQUOTE"><begin quote>Originally posted by: ga1990

There's nothing obvious that I can see wrong with the diaphragm, no visable holes or tears, is there a way to test it?</end quote></div>

Will the rubber diaphragm turn independantly around the slide assy? If so, replace it. Don't force it either. If it turns rather easy it's no good. What I'm getting at is even a new one with enough force could turn, so be carefull not to ruin a good one.

Also, unplugg the limiter rather than just pushing the button. It's the black wire on the rev box(four wires, yellow, green, white and black. I believe those are the colors) Under the front cover.