I purchased a jetkit for my Prairie 400 (2001 w/ 120 miles) and installed it according to the directions for my altitude. After the installation the ATV started and idled fine and seemed a little snappier on the low end. It would hesitate on the low end if giving full throttle from idle. It seemed weaker than stock in the mid-range and high-end. Seemed to be hesitation (cutting out and back fire) from the mid-range to top-end when letting off and getting back to full throttle. Top end speed was down from stock (42-43 mph on a road where I could get around 50 mph stock). I didn't have a lot of time to mess around before we left on a trip last weekend so I re-installed stock jetting and settings. Where should I start when I try the jet kit again? Thanks.

 

Check your plugs, but I think your mains are rich. It is possible that you need to move the needle leaner too.

LEAN usually doesn't backfire out exhaust, it usually backfires out the intake.

Change one thing at a time.