ATV Issues at higher altitudes

[Chuck Piazza]

Hello,

                I have a 2005 Yamaha Bruin 350 atv,  I live in Pennsylvania and  planned on using it in Colorado in a few weeks.  I'm being told by people that I may run into some issues at the higher altitudes ( 6500 to 9000 feet ) since the atv has a carburetor.  Can someone provide some insight?  Thanks.

[Frank Angerano]

That is correct. The air is much thinner up there so a slight adjustment on the air fuel screw will most likely be needed.   

[davefrombc]

Power loss in  carburetted engines is about 3% for each 1000 ft.  of altitude.  You  would  need to  lean  our you engine a little  for those altitudes to  keep it from  running too rich.

[Chuck Piazza]

Is this air/fuel adjustment fairly easy to perform as long as I find the correct screw?   

[davefrombc]

Yes,  the  only  adjustment on most  carbs  is the idle air screw.  It   mainly  allows  proper idling  and  when  set right  stops the  motor  from  stumbling when you go to accelerate .   If  you  will  be regularly  running at those altitudes you  would need  help  to  re-jet  your  carb.  If it  is  just for  a short time , I wouldn't  bother with the re-jetting. You'll lose some  power (18-20%) but unless you're into  full  bore  running  you'll  hardly  notice it .  The worst  you  might notice  is  idle and stumbling off idle  and that  can  be remedied  by the  air screw  adjustment  and that setting is likely  only to  need about  a 1/4 turn from  where it is  now. The  idle  air  screw  is likely to  be  the  only thing on your carb to  have a  thumb screw  for adjustment.  It  is normally  only  about  1 1/2 to 2 turns  out  from  seated.