Alright so the fourwheeler sputters in forward, neutral, and reverse(even holding override) just like it normally does in reverse without holding the override button.

This started somewhat gradually over about 50-75 miles of trail riding, at first it was just a small inconvenience and I would have to roll on the throttle to prevent it from doing it(by doing that I could go from idle to full throttle with no problems.) But after about 50 miles it progressively got worse until I now am unable to drive it past 1/8th throttle without it sputtering very bad. At idle it seems alright, in all gears.

The first thing I did was change the fuel filter and the spark plug. The spark plug was very black.(but also had not been changed in 2-3 years. The fuel filter seemed relatively clean and all the fuel smelt normal and had no sign or feel of water in it.)

It seemed to go decent with the fresh plug, but after just a few minutes of riding it started sputtering again.

I got the fourwheeler home and the new plug was black.

I took the carb off and cleaned where the choke cable goes.
Checked the (k&n) air filter (its clean).
The oil cooler was somewhat overfilled(1/2 qt?). (I drained and refilled with new oil & filter.)
I adjusted the throttle and idle to spec.
The choke was out of adjustment (I adjusted to spec.)
The vent hose from the oil cooler was split by cooler.(I replaced the hose.)
I ran the fourwheeler and it will die when you put on the choke when it is at operating temp. (like it should.)
Drained the bowl on the carb. (no sign of water just clean gas.)

So, It is running too rich. But why? Any Ideas?

 

Sounds like maybe the float is stuck in a high position or dirt in the seat under the needle. Fuel problem for sure.

 

i agree with Mongrol. sounds like a fuel problem. take the carb apart and clean everything including the jets.if that don't help check the valves to see if they're in spec.

 

I took off the carb, the float wasn't stuck, and the jets appear to be clear. But the diaphragm was seperated partially. Anyone know a good site to get a full rebuild kit for it. The only thing I know about it is its a Mikuni carb, with the numbers 50L09b and E9Z8 on it. A search through google turned up nothing. Its not an h.o. either. (don't know if that matters.)

 

Could be wear in the needle jet. Lift the "C" clip one notch and try that....

 

The non-H.O. should be a 34mm Mikuni. At least it was on my '97 and I don't think they ever changed until they switched to the 40mm for the H.O. Try this place http://www.hyperparts.com/wc.d...001~1002~1~0005~000989 It's for a 2000 Polaris Sportsman 500 and they might have the other parts too.

 

I had the carb rebuilt at the dealer, they cleaned it and replaced the needle, seat, and jets. But it is still doing the same thing. (I also replaced the plug before starting it and its black again). I'm thinking its not a fuel issue so much as an oil issue?. Is there any way oil could have gotten on the top of the piston? And if so how do I clean it? Brake Clean?(always worked good to dissolve oil before).

 

Does it smoke real bad? If it was an oil problem then it would smoke real bad.
Check the vent line that comes off the carb and goes up , make sure that it is not plugged up. If that is plugged it could cause a rich condition

 

Thanks everyone for the help.

I finally got it going, and boy it goes good again. Hasn't been able to spin a tire in a long time.(except in low range [img]i/expressions/face-icon-small-tongue.gif[/img])

What finally fixed it was adjusting the fuel/air mixture screw on the bottom of the carb. I started it without the intake on, and drove it around, went really good.
I put the intake back on, and it just wanted to die again. So I knew the K&N was clean, but it has one of those filter socks. I never thought of that thin filter sock causing half the problem. While running the atv(with the air box lid off) I noticed the sock was sucking down onto the filter when I gave it throttle. I took off the sock and it runs like a beauty!

 

Good! A plugged prefilter is as bad as a plugged filter. Should wash in soapy water every two weeks and make sure its dry.