Hi I just got a z400, and it was riding good until the other day. We were riding in a new area in about 8500-10000ft. and my bike started to sputter in all the low ends of my gears. My friends Honda 400Ex ran fine at that Altitude. What the ?!?!!#%@ is wrong. I brought the bike back down to my house and it seems to run fine, anyone know what I have to do?? Thanks

 

When you go to altitude, there isn't as much air so your mixture (jetting) is way off. The bike runs way rich. The post below tells how I deal with it. Actually, I now use TPI Valves (http://www.thunderproducts.com/tpi_valve.htm), installed in the airbox lid. I open them when I ascend (to get more air into the engine), and close them when I descend (to decrease the air). Works VERY WELL, and the TPI is way more convenient than dealing with duct tape.

http://forums.atvconnection.com/mess...word1=altitude

(Post this kind of stuff in the "other atv topics" forum, you will get more hits.)

 

yep; It's all about the jetting

 

Try taking off your airbox lid at that altitude to get it breathing a little easier.