I called a dealer in Durango, CO, and he said I would need a 145 for a '97 Sportsman 400 and a 147.5 for a '99 Scrambler 500. Does that seem right to anyone that's rode at ~12000ft. in CO? He said I should clutch the Scrambler. Is that necessary? What spring should I use?

 

I have a 2000 SP500. I would recommend the 147.5 for it. So a 145 or 147.5 in your case sounds correct.

 

Some of my pictures from Pitkin, CO area were taken around 11,000 to 12,000 feet.

 

Great pictures! How did the Scrambler do up there? Did you have to move the clip up one notch on the needle? The dealer said if I didn't change the spring, the Scrambler would engage much quicker and try to shift up quicker, making low speed riding much different than in Texas.

 

At high altitudes the engines make less HP.....3% less for every 1000 feet above sea level. So at 10,000 feet you are down 30% over your sea level HP. You will have to re-clutch to RAISE the engagement, not lower it, otherwise your engine (especially the 2-strokes) may not have enough power to even engage the clutch at low RPM.

 

Not even enough power to engage the clutch? That seems a little extreme. So is there someone who has traveled to Colorado and rode at high altitude that left the clutching stock? How did it do? We're taking 7 machines, and most of the folks haven't considered any of this. I don't mind to take a bunch of jets and spend an afternoon jetting everyones machine, but installing new springs in all of them is not looking fun.

 

The Scrambler was a 1999 SC500 - purchased and ran only in SW Missouri. It was not jetted at all and ran like a stripped ape clear up to 12,000 feet.

The yellow SP500 in the pictures was not jetted until day 2, but ran fine up to 50mph and up to 12,000 feet on a 165 main jet the first day! I had to take the airbox cover off on day one until I jetted the SP500 on day 2.

Basically, my friend and I brought the jetting tools and jets with us, but went out the first day just to test the capabilities of the ATV's without modifications for high altitudes. The SC500 never needed any jetting. The SP500 did, but would have run fine (though a somewhat lower top speed) without the air box cover.

Don't change your weights or springs for the trip, you'd be wasting your $$$$$. If you are capable of changing your jets on the trails, you might try skipping jetting your SC500 -- it would have been a waste for ours.

However, I would definitely recommed jetting the SC400 per altitude specs.

 

I ride in Missouri regularly. I take my ATV's to Colorado once a year regularly. I can speak with authority on the 4 strokes (see my other posts), but not the two strokes.

I can speak second hand for other two stroke riders I have met on the trails in Colorado, and all they do is change the jet. Period!

I can also vouch that my 89 Trailboss 250 2-stroke has been to Colorado multiple times with the previous owner - a co-worker - and all he ever did was change the jet.

That's my experience - take it for what it may be worth!

 

Thanks!!

 

I have rode Utah and Colorado and only changed jets. Wasting time and money on clutch work. All you are doing is taking in the sights and not worried about speed then just jet if necessary.

Ronnie