I some of my riding around 2600ft my quad runs really great at this elevation. But when I get it up into the mouintains it seems to lack a little throttle response and power, I am assuming this is because of the elevation. My question is, is there a chart anywhere that states what type of jets you should be running at what altitude. I do most of my riding in the mountains around 3500ft but I also can go up to about 11,000ft. I donot want to rejet everytime I go out can anybody reccomend what carb adjustments I need to make and what jets to run in my quad. Something somewhat universal for all of the elevations that I ride in. THe machine is a compltetly stock setup except for the K&N filter.
2002 scrambler 400 4x4 2 stroke.

 

I have just started to really get into carb tuning. I got this link from Modquad. Carb Tuning.Carb Tuning It is good reading and really helps. I don't think you can jet it and forget it with the altitude changes you are seeing, just my opinion.

 

zpnby is right, there is no way to jet for that much elevation change. You could get a dial a jet a compensate some, but it only works if you are lean and need to richen up. You can get a mikuni pocket tuner from Aaen and other places that tells you what jets to use for what elevations and temps. I have one, if you tell me what main jet you are running at the temp and elevation you are at when it runs the best I can tell you what the chart recommends. For Mikuni carbs they recommend a change in main jet for approx. every 25 degree temperature change and a change in main jet for approx. 2,000 feet elevation change. The carb has to be leaned out as it gets warmer weather and the carb has to be leaned out as you get to a higher altitude.

 

G'day zypnby.

Thanks a lot mate for the link.
And thanks to Modquad for sourcing it
It will certainly help weekend mechanics like me.

Thanks from down under, Geoff.

 

Hey aussiequadrider, here is another great place to learn about jetting. I refer to it all the time. I even printed the one above a few months ago and use it often. Ericgorr.

 

G'day NCSrambler.
Thanks mate, fairdinkum have I got some reading to do this easter.
Perhaps there some hope for me yet to be able work on a carb without stuffing it up.

Thanks from down under, Geoff.

 

go to www.mikuni.com and click on the vm series carb.

 

If you don't go through great altitude variations, you can often get by jetting for the higher altitude, and using a dial-a-jet to richen up the mix as you come lower, or for colder weather. About all you would have to really do then, would be change the air screw setting (idle mix), idle speed, and dial-a-jet setting as you move up or down. This is not as good as proper jetting, but far better than trying to use one setting for varying elevations. Also, you only have so much adjustment, so it is possible you could run out of adjustments in the dial-a-jet and still not be able to have it set right for all your riding.

Farmr