I went into the local dealer today to get some jets and find out what they recommend for jetting specs. They said to use a 150 if I want to be able to drive it around town, and a 145 only if I'm above 6500. Local altitude here is about 5500. They also said that they don't recommend even messing with the needle jet or clip settings. Is that really correct? I thought those were necessary changes for 1/4 and 1/2 throttle.

How much of a hp difference will there be between a 145 and a 150 main? Is it going to be worth messing with the 145 main if we know we're going to be a t 10,000 all day?

 

I don't have to tell you that the higher the altitude, the thinner the air. Same logic for your ATV, when the air gets thinner the A/F ratio gets richer when set for lower altitudes. For every given engine, it's going to like a certain A/F ratio at which point it makes max horsepower. However, altitude, temperature, humidity all play a role in that formula and make that sweet spot a moving target. Your dealer is recommending what Polaris does in its owners manual. That jet change may not just increase power in higher altitudes, but may keep from fouling plugs and prevent other drivability issues. Your buddy may or may not have problems at altitude, but he should bring along that jet and some tools.

 

I left the stock jetting alone on my sportsman. I have been up at 11,000+ ft but it is just a mountain pass. I did notice a power difference. but it wasn't like it wasn't going to make it or anything. I also plan on going to moabthis year which is lower then I ride. I spoke with my dealer about having to re-jet for the lower altitudes and he said that I would be okay as long as I don't run WOT for long periods of time. My advice would be to find a middle ground jet for that then leave it alone. The middle ground has to take into consideration the seasons along with your elevation. You will run leaner in the winter and richer in the summer. Find where you spend 90-95 percent of your riding and jet for that.

 

At 5000 feet, my sportsman 600 really drank the gas so if you are going to be riding at 6500 a lot, I'd change jets because of fuel economy and possibility of fouling plugs.
I'm normally riding around 1000 ft so I could see the difference in gas mileage.