During major elevation changes I know you typically have to rejet the primary jet for full throttle, but do you also need to change the needle-clip position for midthrottle operation? I mean if you go up very high in the mountains and by the charts you must drop down 2 jet sizes on the primary, then do you also need to lean out the midrange by raising the needle-clip position? Or is the midrange automatically leaned out by the reduction of the primary jet size?? Do drastic elevation changes ever require rejetting the pilot jet or can that typically be taken care of by the airscrew?

Thank you all for your help!!

Doug

 

I'm going to the Black Hills this summer and was told to drop my main 3 sizes and the needle one slot on our Sport and Scrambler 400. They didn't say anything about the pilot. That's for riding up to just over 6000 ft asl. We currently ride at under 2000 ft asl. Like you, I had thought a couple sizes on the main would be enough, but this is from folks with experience.

 

Thank you for the information Joyrider. Wow!! 3 jet sizes for a 4000 ft change. I live in Billings, MT which is about 3200 ft, but most of my riding is between 6000 - 9500 ft up in the mountains. When I went elk hunting earlier this fall I dropped down 1 size on my main jet, and never touched the needle-clip at all. I was at about 8500 ft elevation and my 350L 4x4 just seemed very sluggish and would not develop normal RPM's. I am sure I was running at least several sizes too rich on my main jet and that would explain why it seemed so sluggish!! When I got home I pulled the sparkplug and it appeared very black and oily so I am sure it was running rich. I have been a little hesitant to lean out the midrange very much thou as I have heard that you can be running rich at full throttle but still be running lean at midthrottle, and risk burning up a piston. I guess I need to grab a handful of new plugs next time I go out and try to do some plug-reading at the various throttle openings; idle,cruise and full throttle.
My jetting problems are compounded because of the addition of

1. I added a HotSeat xplorer pipe ( recomended 2 jet sizes larger on main)

2. V-Force Delta 2 reeds and valve ( somewhere on this forum someone suggested that this reed actually required 1 jet size smaller than stock?

3. K&N filtercharger and outerwear for dry riding conditions.

4. Installed a UFO on my stock 34mm carburetor. ( I've heard these can make it difficult to get carburetor tuned right, and difficult to do an accurate plug reading.

Again thanks for your input Joyrider, I will definately consider leaner jets next time I ride that high again!

Doug