Jetting for 8,000 * ft

01 426-Has anyone ran stock jetting at this elevation, if so, how did it run? Can you adjust the airscrew and get it working good? The reason I ask is I ride with 3 guys on XR400's with stock jetting and they run grea at this level,

The temperature also affects the jetting. What is the temp there? The altitude will make your bike rich, but if it is cold, the temperature might be cancelled out. But if it is hot, you may have to lean the bike out.

I don't think you'll get very good results trying to run stock jetting at that altitude. A simple way to get close, is lean out your main jet. I've got my bike jetted to run well at 6,000 ft. When I head up into the high country, I drop my main from a 160 to a 158. I believe my PJ is a 45, and I'm about 1 1/4 turns out on my PS. But like MXRider says, there are more variables to take into consideration, including temp, altitude, and atmospheric moisture. This is what works for my bike, so it's only a guide line for you.

Dodger :):D

Temps are between 50 & 80 and colder at times.

I have a 02 YZ426 and I recently rode at 8,000ft and above with a FMF Q pipe and it would barely run. I've found that the Q pipe really chokes off the motor at sea level or any altitude. So just like the other guys have stated set up and conditions will really affect your final decision. My bike needed a 155 main jet before it would run half ass desent, I left the pilot stock because I didn't have any.

Originally posted by T-Gore:

01 426-Has anyone ran stock jetting at this elevation, if so, how did it run? Can you adjust the airscrew and get it working good? The reason I ask is I ride with 3 guys on XR400's with stock jetting and they run grea at this level,

If your bike had an airscrew it may help, but it does not :)

Here is what worked at 7 to 9 on my ’01:

158 main

38 pilot

75 PAJ (this is the stock WR size)

EKQ #3 (this is the stock ’00 needle, which I happened to have laying around, I suppose the stock EJP would work in a pinch but you may need to try clip # 2).

200 MAJ (this is stock, but next time I will try a 180 MAJ).

1.25 turns out on idle is I think where I ended up (this is a fuel screw BTW, not air).

The biggest change that gets rid of the most annoying richness and only requires one part would be the pilot jet and dropping the needle a clip or two. At the very least you should try that, you will not be disappointed I promise.

Hope this helps.

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