[UteMachine]

I am at wits end with this problem. Here are the vitals

Bike- 04 CRF 450 R

Conditions- Altitude from 4300ft Salt Lake City to the mountains at 7500ft, humidity around 37%, temps around 80-100 degrees, trail riding.

Modifications- Thunder Alley full exhaust with quiet core insert.

Current Jetting- 165, 42, and the clip is dead center.

Running Issue- Whenever I ride in the mountains, give a burst of throttle, then pull the clutch in, it almost stalls or does stall. If I wait for about 5 seconds the idle comes back up. I've been told I am way too rich. I think it started around the time I put the exhaust on and I have never touched the jetting. Playing with the fuel screw does nothing to solve the issue.

Problem variances- The issue seems to go away when I come down from the mountain to an altitude of around 4400ft. In fact, I usually have to crank the idle up while I am up the mountain, and by the time I am back down the idle is really high. The quiet core insert made the problem worse when I installed it.

Thanks for your help!

[JAWS]

Your description does make it sound too rich. The main thing that changes with lower altitude is the presence of more oxygen. The JD kit has a needle and setup especially for altitude. You could give that a try. I suggest that you call him and inquire.
Joe

[paul turner]

We have the JD kit in Pat's 250r, and it runs flawless up to 9500'. I just drop the main one size for the KM trips only, then tweek the fuel screw at camp warmup. usually just in a little bit.

paul

[UteMachine]

Thanks for the input guys. I was trying to get away without doing the JD kit. I went to a 160 main and up one on the clip. If that doesn't work I will get the JD kit. Thanks again!

[Skoot22]

what i have found is usually a main jet is all you need to adjust at higher elevations. a 160 should help.