Riding High (12,000ft)

[mideastrider]

My neighbor asks me what to do about his Honda 350 Rancher 4-wheeler. We live at around 950ft above sea level and it runs fine. But he took it out West on a hunting trip at about 12000ft above sea level and it fouls plugs.
I have never dealt with that kind of altitude change and don’t really know what it needs. Has anyone ever dealt with that much of an altitude change and if so what does it take to correct it?

 

[yamarider88]

i live at about 5,000 ft above sea level and ride anywhere from 4,000 to 10,000 and you absolutely have to re-jet there is no bandage way to fix the problem machines have with carbonated motors and altitude.

 

[mideastrider]

How much of jet change does it normally take to correct.1 or 2 jet sizes take care of it or more. I am sure his 4-wheeler has stock jetting.

 

[yamarider88]

on all the bikes and 4-wheelers my family owns we usually go down 2 main jet sizes and then 2 or 3 for the pilot jet but it really needs to be tweaked with and played with at the altitude you are jetting for. so we just tune our machines for where we live at and then its pretty safe to ride all the places we go. we live at about 5,000 and so thats what we jet for and it runs much better at 8,000 with 5,000 jetting than it would 8,000 with sea level rich break in jetting which is what most stock jetting is if you know what i'm talking about. you could also try tunning for the altitude by using a chart or guessing but with my experience in that it usually ends up still needing to be worked on. but one pilot jet size usually covers about 2-3,000 feet or so to answer your question but you really can never tell it's all different depending on what brand your carb is and what brand jets your using there are a lot of factors involved in the equation.

 

[mideastrider]

Thanks yamarider88 that gives me an ideal what he needs to get. Sounds like he needs to set it up at least 2 sizes down and maybe take a couple more just to fine tune with.

 

[yamarider88]

yep thats exactly right.