I have a 1998 Big bear 350 that runs great other than on very light throttle. The problem is, I can give it light throttle and it tries to bog slightly and then as you start to give it a hair more throttle is lunges or surges either forward or in reverse. It makes it tough to load up ramps and such because you can't take it slow and easy. When you are giving is more than 1/8-1/4 throttle it runs great. I'm sure this is a jetting issue but I wanted to get some opinions on how to solve this?

Also after the big bear has gotten good and warm and shut it off, it will give a slight gargle back fire. not a loud pop but more of a airy backfire. Any suggestions?

 

First thing is take the carb off and clean it. Used YouTube search to show you how if you never did it before.

 

I took the carb off and completely cleaned it a couple months ago trying to solve the issue, but it didn't solve the problem.

 

Make sure that idle jet is clean. I had similar problems with my 93 Big Bear, Carb cleaner would not clear out the jet. I attacked it with a bristle from a brass wire brush and a compressor. I could not see light through it when it was cleaned, though I could blow through it and feel air on the back of my hand.

Fixed the problem for me. You said the carb was cleaned. Did you verify that the jet was clear?

Matt B

FYI I cleaned the carb without fully removing it. I removed the hoses and rotated it about 90 degrees and cleaned it in place.

 

The only way I do it is the wire through the jets. Can,t count on carb cleaner or soaking clearing those passages.
Disassembly and Cleaning of a Mikuni Round slide Carburetor

 

Well I am still having the issue I mentioned above. I have taken the carb back off and cleaned the idle jet thoroughly. I took the pilot screw out and cleaned it as well. I screwed it back in exactly like I had it. Could the Pilot Air Screw be the culprit? I screwed it back in the exact amount of turns as when I took it out. If it is bogging at 1/8 -1/4 throttle and then lunging does this sound like a lean or rich condition?

 

Well I tried adjusting the pilot screw today and it did nothing to help. I was able to screw in the pilot screw all the way and the atv didn't die. Does this mean the pilot jet is the wrong size? I also unscrewed it quite a bit and didn't notice much change?

Any help is appreciated.

 

Any ideas?

 

I don't know a lot about these things, but I feel for you. Should there be an o-ring on the pilot screw? Is it cracked or missing? I am thinking that would allow air to bypass the idle jet - too lean to run properly, but OK when the main jet goes to work.

Don't yell at me if this does not make sense - I am really stretching here. I would not think a jet would be the wrong size unless it was reamed-out mercilessly by a piece of wire, the quad was way out of the altitude it was calibrated for, or someone changed it.

Did this problem develop or did the quad come to you this way? If a sudden development, I am thinking air leak from bad gasket, seal, o-ring, or the like. If gradual, maybe something is just plain "wore out." At the point you are, I would likely take it to a shop and pay. If something gives me too much frustration, I lose faith in it and replace it or find another hobby, so I am careful to know when I should employ the services of pros.

Matt B

 

You've tried about everything you can do. If the adjustment doesn't affect it there could be a leak from a gasket. I'd go the profession route now and have them also check if the jet is the right size or worn. No fun if it don't run right.