Carbureted Bike & changing altitude

[Bernster]

Mike,

I'm planning a ride from Portland, OR to Butte, MT. Ultimately, I will have an altitude change of about 6,000 feet. I have been told I should expect to have to make adjustments to the carb in order to keep the bike running. Is this true? My bike is a 2003 FXD. The only modifications to the motor are Screaming Eagle Slip-ons and carb rejetting that Latus does at the same time. I would expect some decrease in power due to the changing (increase) in altitude, but will it really be necessary to mess with the carb?

Bernster :o

You should not have to make any changes to the carb to correct for altitude. The CV style carb actually effectively compensates for altitude since it works on the pressurre difference between the throttle bore and area above the slide. Both of these are affected by changes in altitude thus causing a change in the carb. However, we find that most carbs are way overjetted and some riders do experiance a need to make jet changes when at high altitudes. This would indicate that their jetting was incorrect to begin with. You are correct in that you will experiance a performance drop at altitude simply because the motor is pumping less air since less is available. Also, the carb can only compensate so much (as a mechanical device) and that is an approximation. If you were to stay at a changed altitude, then permenant jet changes would be required to get the best state of tune.
;) Mike