met a guy on an atv jambori that was having problems at high altitude keeping his quad running..it would start run for a minute and die this was going over a mtn. pass at about 10k anyway to make a long story short. the same guy was in my group of riders a few days later.i asked him if he figured out his previous problem.he told me yes and said the problem at high altitude was caused by his k&n airfilter..apparentely the better breathing k&n filter was causing a problem by confusing his efi computer and it wasnt adjusting for the extra airflow. he switched back to stock filter and bike ran fine over the mtn. passes. i was wondering if anyone has ever herde of this or had this problem.also i should mention that it wasnt a polaris the guy was riding. it was a honda rancher or maybe a forman? i was thinking of putting k&n on my bike but now im not sure because i often ride over 10-12k mtn. passes

 

Actually in theory too much air is not an issue as you are ascending. The higher up you go, the more air you need to keep the fuel / air mixture at the proper ratio if the rate of fuel delivery does not change. One way to compensate is to change to a smaller jet (less fuel to go along with less air) at higher altitudes (for carburetor equipped units). Another way is to increase the air flow to keep the fuel / air mixture the same when the fuel delivery rate has not changed (no jetting change). However on a FI unit (depending on the computer / sensor setup) I can see where changing the airflow rate can confuse the fuel / air mixture computation...