My son has a 2000 250 Trail Blazer. It has a problem that it constantly fouls plugs. It also is backfiring through the exhaust. It backfires so violently that it blows the exhaust off at the jug and past the next joint. I just had the jug bored out .5mm and a new piston and rings put in. I need some help. Could it be that the main jet needs to be one or two sizes leaner?

 

how is the float? is it set right and not flooding out the engine. the backfiring could be igniting the excess gas in the exhaust. if its getting that much gas it must bog a little as well. check to make sure the air filter isnt plugged or the air inlet.

 

Thanks for the reply. I think I found the problem today. The pilot jet had worn grooves into the seat. I replaced them both. No more backfiring. Now I notice that it seems like the motor doesn't top out correctly. When I'm hill climbing the motor stays at relatively low RPM's even though I have the throttle pegged. Any ideas?

 

check to make sure the slide is going all the way up in the carb when you have it wide open to make sure its opening all the way. make sure the air screw is set right and the air filter is clean and not restricked.

 

The slide is coming the whole way open. I spent a couple hours trying different air mixture screw settings. The best setting seems to be one turn out, but I'm still having problems with it bogging when I dump it to full throttle. I tried moving the needle jet clip up and down with no drastic change. I still have the additional problem of the ATV not reaching top end on hills. It will top out on the level, but not while hillclimbing. Should I try a smaller pilot jet and a bigger main jet? Any other suggestions?

 

forget it i need to read better.

 

hows the belt, clutch weights or rollers worn ect....

 

first...is it all stock wiht all stock jetting or no? could be a variety of things

 

I bumped up the main jet two sizes today and the ATV is running much better. I think the backfiring was occuring when th engine wasn't properly warmed up. After I put in the new main jet I took it for a ride up our hill. It went right up at full throttle with no hesitation. I'll keep my fingers crossed. Thanks for all the ideas folks. I'll keep everyone up to date.

 

Now that its running better, do a plug check @ full throttle. Let the machine rev near top speed & cut ign., stop & pull the plug to see if its still too lean or rich. A clean filter is also a must for this. Proflow