I am new to this forum and new to adding performance upgrades to my quad. I recently installed a K&N air filter with an HMF slip exhaust and a Pro Cricuit header and the Dynojet re-jetting kit. I first installed the filter, then the HMF slip on and it ran fine. Then re-jetted it and installed the Pro Circuit header and it started to backfire when I would let off the throttle. The jet size now is a 170 and the needle is at grove number 3. I initially installed the the 146 jet but the a neighbor suggested to go to 170 because of the full exhaust. Just wondering why it is backfiring and if anything can be done about it?

 

is it a stock pilot jet?

did you try increasing the air fuel screw to richen the low end?

 

Tried that but it still continued to backfire and a dumb question. What is the pilot jet. Being that I don't know I am pretty sure it is stock. Just replaced the main jet

 

The pilot jet controls the gas flow in the idle circuit, and it sounds like its too small. Go at least one size bigger, and readjust the mixture screw.
Backfire on letoff is a sure sign of a lean idle circuit, also check for intake leaks, as that could lean out the idle circuit too.

 

yep pilot jet

 

JBlatch,

One of the most common causes of backfiring while letting off the throttle is an air leak at the connection between the cylinder head and the exhaust flange. I'm not saying that's definetly your problem, but, its not hard to check it and you haven't lost anything if its not the problem.

HTH

Brian C.