jetting and elevation above sea level

I have a TTR230, and have been reading all the stuff about re-jetting, air box mods, and so on. I assume that my bike, which is an '07, was factory jetted for riding at sea level (and maybe in California, also).


Where I live and ride, the elevation above sea level is about 2500'. How should that affect the way the carb works ?? I know that the higher you are above sea level, the less dense the air.... therefore it would stand to reason that my bike should need more air for the 'sea level' jetting setup to work. The bike acts like it wants more fuel, but is re-jetting to larger jets the way to go ??


Help !!

You are fine at 2500 ft

ok how about 4000-6000 above

If intialy jetted 'perfect' at sea level, for your average regional temps / humidity levels,

riding in : higher elevations, warmer ambiant temps and higher humidity all makes your engine run richer.

You compensate with leaner jetting to adapt to these changes.


2-strokes like YZ-125/250 are even more affected by these changes, as the fuel also carries the lubricant in the premix.

It is not un-common to re-jet at every 10°F change in ambiant temps to keep an engine in 'perfect' jetting.


Yamaha doesn't have specific regional jetting specs. for different locations in the US market,

they have a basic single US spec. that they figure will work 'ok' everywhere but of course could be fine tuned to your actual conditions.


A TTR type trailbike should have a wide range of operation before a change is required,

but going from 2500ft to 4000ft+ sounds like it would require some carburation adjustments.

Edited by mlatour

Here is a good read on jetting.


About mid way down there is a formula you can use to determine if you need to re-jet due to temperature and/or altitude. 

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