My wifes atv, a 97 Trailblazer 250 2-stroke, has developed a problem the past couple of outings.

This is the senario from the last outing-
This last outing after about 1/2 of riding when it got good and warm it started to backfire through the carb and bogged down when you tried and press the throttle in gear(fwd/rev) at first, but it would still rev up fine in neutral. But, then after trying a few things it had gotten worse and would just bog in neutral as well if you hit the throttle. And when I say bog, it will not stall, but when in gear for example it will not even move, just backfire and/or kind of go "brrrbrrrbrrr" in a deep graoning manner. The plug looks clean, but I going to try and get a new on asap to try it. I took the airfilter cover off when it was doing this to see if the filter was providing restriction but that did not help. The fuel in the bottom of the tank was a couple months old, but I filed it with fresh before leaving so after a 1/2 hour I do not think that is the problem and I use premium only. I am going to try and bypass the inline filter to see if anything changes and I need a new one.

If anyone has any advise I would be very grateful. I tried to search here and on the web, but most of the backfiring posts seem to deal with backfires through the exhaust when you let off the throttle.

Thanks,
Nate

 

Generally, a backfire (through the carb) is caused by a lean condition. After you try a new plug, and the problem still exists, you might want to pull the carb, and check for clogging, especially in the main jet.

 

when you pulled the plug out, was the tip or the porcelin ( the white part) white in color? it should be golden brown give or take. becareful if you are running lean, which does make it backfire, you could melt your piston and burn your engine.

 

i use 98 octane gas in my wheelers, there all 4 stroke tho...when i use the cheap $hitty gas they dont backfire..maybe that will help too

 

higher octane gas does a little cooler, but we only run 89 in our t.blazer w/ no problems

 

these guys are correct also check the oil tank and if if plugs you could have the same result

 

when it starts to bog, throw the choke on, does it improve?? how's your exhaust? is it clogged???