We will be riding from 9000-12,500 ft. We will be riding 3 Sportsman 400's, Explorer 300, and my Scrambler 500. All these machines have stock jetting and air filters. Any ideas on the range of jets I should buy before we leave? I have to buy enough for all the machines so I'd like to only have to buy ~2 for each. Will I have to change pilot jets too? I'll be doing maintenance on them before we leave and thought about going with a K&N or Uni filter. Would that be enough to overcome the need for jet change?

 

Steve10

I rode the paiute trail lat oct. all the way up to 11,090 ft with my sportsman 500, it started sputtering above 9000 ft,so i stoped and removed the air intake snorkel reducing the resriction and it was perfect for the rest of the week, plug looked just like at home (sea level).

i also have a K&N

Rick D

fourwheeler page

 

Your 2-stroke buddies had better stock up on jets....they are going to be affected waaaay worse than you.

 

I went to Red River New Mexico with the 400 Sport (2 stroke) last August and could not get it to run right. I went all the way up to a 270 main and played with the mixture and it never would idle. I'll be going back again, so if anyone can give me a recommendation on the jetting in the high altitude, I'd appreciate it.

The 4 strokes will not be affected nearly as much. I took a Honda 250x last summer also and it ran great with only a main jet jump.

 

I've heard of more people having problems with their jetting going East or west then north or south.

 

The higher altitude you go, the SMALLER the jet sizes....not larger. At high altitude there is less air, therefore you need less fuel. On my old sled we would unload at 1400 feet and spend the day at 7000 feet. This usually required a jet change 1/2 way up the trail and one at the top of the mountains. On the 3 cylinder 600 engine with 34mm carbs I ran 220 jets at the bottom and 150 jets at the top.

 

I have a 2001 SP500HO and a 98 Explorer ( 4 & 2 stroke)and had lots of problems on trips to Colorado (10,000+ ft.) until I installed Dial-A-Jets on both. This enables me to adjust for altitude and temp easily without changing the main jet in the field. Made by Thunder Products in MN. The only way to go if you ride at varying altitudes and temps!

 

That's pretty cool, but expensive. I guess I'm going to unload at ~9000ft. and jet them there. Hopefully we won't need to do it again when we get to the top. Should I count on moving the clip on the needle up one on the 2 strokes? How about the 4 strokes? Since that's more of a pain, I might do that on all of the 2 strokes before we leave so I only have to remove the bowls on the trail.

 

The needle valve controls the mid-range only so you might want to change the main jet that controls full throttle. I think the stock main jet is 155 or 152.5 on your SP500. You'll need a smaller main jet (147.5 or 145) for altitudes of 8,000 ft and up. My SP500 HO ran very poorly at 7,000-8,000 ft with 152.5 main jet - about 60% power, very sluggish and stalled frequently. I frequently go from 3,000 to 8,000+ ft. so Dial-A-Jet is better than changing the main jet each time. For one-time trip, take a pocket full of jets and some tools.