Originally Posted by queen of spades

2007 KLX250S (std bore)
4700 miles on odometer (bike's condition reflects the mileage)
~4000 ft above sea level
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KDX200 snorkel
K&N air filter
Dynojet 2152 kit with 128 main
All smog crap removed and capped
OEM header
FMF Q4 slip on with 1 1/8" quiet core


Bike idles smoothly and once hard on the gas it pulls as well as can be expected from a 250cc bike. Somewhere between open and idle is a catch.. the bike stumbles a bit almost like a two stroke.

Note that if I accellerate from idle to full throttle, the bike pulls clean. The stumble/catch happens when the throttle is chopped and I reapply throttle. On the ride home yesterday, the stumble after chopping throttle caused the bike to die. It started back up with little fuss.

What could be happening?