CRF250X with JD Kit cutting out at Full Throttle

I have a 2005 CRF250X CA model that is cutting out at full throttle after I installed the JD kit. I ride in So. CA and have the following modifications:

Closed Course airbox modification

Air Filter Screen removed

Twin-Air flame retardant filter

Power Now & Power Now Plus

1/2" hole drilled in the end of the exhaust diffuser

Zip Ty fuel mixture screw backed out 2 turns

I installed the kit's red marked needle with the clip in the 5th position and have tried both the 160 & 165 main jets.

Should I change the main jet to a smaller size?

The top-end stutter could be the rev-limiter, or possibly too rich of a main jet. They have a similar symptom. The Power-Now can make a difference in full throttle jetting too. Try running the kit's #158 main jet and compare to see if it makes as much power and if the bike revs higher.


I run the power now with JD kit and the main needs to be leaner with the Power now installed. I am usually 5 to 10 sizes smaller on the main. It will fix your stutter problem at full throttle. :cry:

I installed a 152 main jet and the the bike runs alot better at full throttle. Its not perfect and still cuts out sometimes at full throttle. Also I went riding with my friend who has a stock 250x to compare. My modified 250x is quicker on the low end, the mid-range seems slower, and the top end the same.

What should I try to improve the mid-range?

Should I try the 155 or 155 main jet?

Also should the bike be faster at full throttle or just quicker getting their? (We rode next to each other at full throttle on a fire road and the stock 250X was just as fast.)

Does his CRF250X have the Power-Now?

Adding the Power-Now plate(s) in your carburetor venturi will reduce some of the airflow and top-end that you gained by opening the airbox. This thread is becoming more about jetting with a Power-Now than the kit. You will need to make test runs and compare to make more gains on the top-end power.


My friends bike is a completely stock 2004 250X. (NO POWER NOW)

What do you think about the mid-range. Should I change the position on the needle jet?

I can remove the power now & power now plus and change the main jet, what do you recommend?

My modified 250x is quicker on the low end, the mid-range seems slower, and the top end the same.

The Power-Now is aimed at low end throttle response. It's your choice whether or not the benefit is worth a tradeoff in mid-range or top-end. You will need to test the clip positions to find which is best.


(Note-I do not run the Power-Now in my CRF250R, but have tested bikes back-to-back with them before.)

What did you notice when you tested the bikes back to back with the power now off and on?

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