High altitude tuning

[Ricksvmax]

Hi everybody,
I recently moved to Leadville, Colorado, where the altitude is 10,200 feet,
from Michigan, near sea level, standard carb tuning. My Vmax is a 1999, with Dale Walker, "Holeshot" exhaust, and his stage one jet kit. Spring is FINALLY, getting here, and I need to tune it for the altitude, does run, lacking power of course. Altitude from here goes down, no matter the direction I go, but will be generally be from 8000 feet to 10,000, trip to denver will go down to 5000 feet.

I plan on opening up the air jets, to accomadate the thin air, but I wondered if anyone has some tips on the subject, that may help me from guessing too much.

I appreciate any help,
Rick

 

[vmaxinID]

Is there a dyno near you can do some pulls to know where you're at?

I live at 5,300ft and have reduced my main a few sizes to help.

Remember the higher you go the richer you go. The lower the leaner.

I estimated my lowest elevation of travel and my higest, then tuned to the middle of the two.

P.S. I can't think of a higher elevation anywhere in the USA, damn when you get high, you get high.

 

[Ricksvmax]

Hi, thanks for the input. No dyno in the area, that I am aware of, probably Denver, little low to really help, will have to do some looking.

You say you had to change the main,, excuse my lack of knowledge, that would be the stage 1 jets that I installed, go back to stock maybe? Oh, I forgot, also have the K&N air filter installed.

As I said, my carb knowledge is limited, is there an adjustment for more air in, a jet, or is it only less gas in?, I forget.

Where do you live, at 5300 feet? If you get the chance to see Leadville, the views are awesome, two 14,000'+ peaks, greet me every morning. Cant wait to see them and more from the bike.

Rick

 

[vmaxinID]

I am not the best on the site but heres what I know. More will chime in soon.

high elevation=thinner air=richer
K & N=more air=leaner
bigger mains (i.e. jet kit)=more fuel=richer
Full exhaust=more air out=leaner

So you are most likely a bit on the rich side. How much, I don't know.

If I had to guess, and please take this with a grain of salt,
I would return my carbs to stock, and then reduce my main jets (x4) by 2 sizes, and then shim my stock needles as needed.

Hey Mark, what was that formula for mains?
Something about one size per so many feet elevation?

 

[Shuriken]

I'm running my bike at 5700ft right now. However, there are mountain passes of 9000ft and sometimes I take the bike down to 4000ft. So my situation is a mess as I don't want to cook the engine, but I also want power. I'm using 147.5 mains right now with the stock exhaust and filter.

You notice the sponginess/lack of power at your elevation as you mention, so I'm sure you'll want to go down some steps on your jetting. What do your spark plugs look like? Soot black?

 

[user 773]

You should drop in on these guys:

www.pythonmotorsports.com

Stopped in while I was in Denver (not on the Max) and they were great guys to deal with. I suspect they may be able to help with your tuning and dyno search.

 

[Ricksvmax]

Thanks for the input, have not yet ridden here, so have no input on plugs or much beyond the couple minutes from unloading bike to parking it, that was a few weeks ago and it was snowing sideways. Warm weather comes very late here. The last below freezing temps average july 4, or so. Left Vail today at 5:30 pm, was 78, got to leadville, it was 48 and raining, very strange weather at the top of the Rockies.