I did a post on this back when. I have since gotten this system down to a science, so I thought I would post again for new readers who missed it:

We ride a variety of altitudes from below sea level (low desert like around Glamis), to the High Sierras . Sierra rides typically start in the valleys at 4,000', and go up to over 10,000'. THAT IS OVER 6,000' OF ALTITUDE DIFFERENCE ON ONE RIDE!! If I jetted for the high altitude, I would be lean (bad for the engine!) at lower altitude. And, if jetted for low altitude, the bike runs bad at elevation.

On the Rancher for example, my solution has been to jet the bike for sea level, and drill 8 one inch holes in the airbox lid with White Bros./UNI airbox filters in them. At sea level, I TAPE OVER ALL THE HOLES WITH DUCT TAPE. As I go up in altitude, I begin removing the tape to give the bike more air. At 4,000' I have 1 or 2 holes untaped, and at 6,000' I have 3 or 4 holes open, and up to 10,000' 6 or more open, etc. You get the picture........ You have to just play it by ear and experiment to see where the bike runs best at your altitude. One word of caution. BE SURE TO REPLACE THE TAPE AS YOU DESCEND!! OTHERWISE, YOU WILL BE RUNNING <u>LEAN</u> WHICH WILL DAMAGE YOU ENGINE!! And, with the tape off, your airbox is no longer sealed so be careful in deep water!!

 

This is not to contess your line of thought, but I will add my own experience with regards to "high alititude" riding. My bro-in-law and I have twin "00 Kodiaks in all respects. We went out to Utah's Paiute ATV Trails this last summer to ride the mountains. We had never ridden up high like that, Wisconsin "high" riding is no more than say 1500-1700ft at best. We knew the lower limits started at around 4500-4800ft, with the upper reaches to 12000ft. We were going to ride and camp every night, so hauling all our camping was going to be a necessity, extra added weight on our machines.

We did as much research as we could to determine if we really needed to have our machines "re-jetted". I talked to several dealers in Colorado, with varying opinions. Basically, we were told we would be okay up to roughly 9000-10000ft before we noticed any negative effects in performance from the alititude, if we did not re-jet. So, we decided to take a chance and not re-jet the carbs.

We covered over 200 miles on the Paitue, without a single hitch. We reached the uppermost part of the trail with a gps reading at 11952ft. No real problems, just alittle bit of sluggishness in the machines. WE saw a side trail heading up even further yet, and decided to go for it until the Kodiaks said " no more". At this point we are above the tree-line, nothing but small shrubs and lotsa and lotsa rock. WE climbed that trail loaded with all our gear, boy was it slow! We made to the top at 12229ft , but the Kodiaks really had to work at it. They hiccuped and burped a few times, but didn't give up. What a trip!

This got alittle dragged out, but back to my point. Four-stroke machines are not so subject to high alitiude operation as the two-strokers are. You can run higher with less noticable side-affects on a four-stroke. Should we have re-jetted? Perhaps. It really depends on your ride, type of riding, and your tolerance to some performance loss.

recon.....Glad you found a system/technique that suits your riding needs! Happy Trails!

 

Jetted for sea level, use to be by the time I reached 10,000', when you let off the accelerator the bikes would stall and be difficult to restart. At that point I had to take off the airbox lid and things would be fine!! Then I got the idea to just do it incramentally, and open up the airbox gradually with a bunch of holes, as I ascended in altitude.

For a one time short trip like your Piute Trail story, you can get away with it. But, my last ride was at 6,000', the one before that was BELOW sea level, and the one before that was at 4,000'. When you live with these kind of altitude changes on an EVERYDAY BASIS, you need to have a creative solution!!!!

 

The original post is old, and I have since developed an even better method-----------

I now use the Thunder TPI Valve (http://www.thunderproducts.com/tpi_valve.htm), instead of the holes and duct tape thing. Principle is the same. Open the valve as you ascend, and close it as you descend. The TPI is just way more convenient.

You are just adding more air, instead of jetting down for less fuel. The end result is the same. The system works great!