Long story short, I foolishly let my atv sit without stabil for 4-5 months. Starts great. Coughs, backfires at idle. Runs rough at low speeds...more backfiring. From about 1/2 throttle to full throttle problems seem to clear up for the most part. As soon as I let off the gas and begin decelerating..more backfiring. I've had an aftermarket exhaust and CDI on it for 4 yrs. Has always ran great til now.

If I choke it slightly at low speed, it does run better. I thought the carbs were dirty at first...but I can't imagine dirty carbs, and it acting like its running rich. I'm no mechanic.

I took it to Kaw dealer, and after cleaning carbs, and fuel system they concluded the stock main jets need to be one size smaller. Their thinking was because of the aftermarket exhaust. I thought an aftermarket exhaust would cause it to run leaner? I wasn't convinced the dealer had a clue, so I took it home with it running as it did when I dropped it off.

Now, all of a sudden, at idle, gas pours out of the carbs!!!! I plan to take it too another Kaw dealer next, but wanted opinions from you all who might have had similar issues. Thanks Oh..and I have plugged in my stock CDI, with no change in the problem.

 

your carbs needs more cleaning,
the pilot jets are dirty..their is one in each carb
they have very small holes in them and they have to be perfectly clean if not,
you get just what you described
as far as gas pouring out ....your floats stuck for some reason
good luck

 

ditto

Also, a person would typically need to go up in jet size for an aftermarket exhaust.