426 backfire and hesitation

On my 426 I get a hesitation when I juice it hard....

Then when letting off throttle in gear I get some back firing...

Bike has little hours on it as I bought it , then moved to different state, then opened a business etc etc. so my bike may have 30 hours on the motor.

Any ideas? This is my first 4 stroke MX bike, before this bike it has always been 2 strokes, so Im a novice to this style of bike.

Thanks for any input.

The backfiring (lean-popping) indicates that the it is running lean, but doesn't necessarily mean that it is running too lean...a little bit of lean-popping is not unusual.

As far as the hesitation when hitting the gas goes...that is a normal symptom also that can usually be adjusted to a minimum with the fuel screw.

So my answer is that if it is not lean-popping too much and if you can adjust your fuel screw and idle to minimize the hesitation or bog then you should be okay. Beyond that it sounds like you need to make a jetting change. I am by no means a jetting guru so I won't try to address that but there is a whole section here on TT regarding jetting. Do a search on the fuel screw to find out how to optimize that adjustment.

Good luck!

You may want to pull the carb and clean it. A partially restricted pilot jet will cause the same symptoms that your having. FCR's are very sensitive to dirt, gum and varnish.

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