Snowmobile Fanatics banner

1 - 4 of 4 Posts

·
Registered
Joined
·
648 Posts
Discussion Starter #1
If I understand correctly the main jets are what takes over above 1/2 throttle, then what do the pilot jets do. When and why would you want to change them from stock? If you change them do you typicall go lower?

Thanks,
 

·
Registered
Joined
·
5,400 Posts
The pilots are from 0-25% of throttle. The needle jet is from 25-75% of throttle and Mains are 75 to 100% of throttle.

Changing jetting is not as simple as just going lower. If you go to low you burn down the motor, so you need to find out what you need. Typically a run at the determined throttle for an extended period and a hit shot of the kill switch will tell you what you need to know. Then you pull your plugs and take a look at them. You are aiming for golden brown. White is too lean, so you would need larger jets. Black is too rich and smaller jets would be needed. Then you can take a look at the piston wash. Silver areas on the piston indicates the the mixture. A thumbnail size area cleared off by the mixture is what we are aiming for. Lean is tough to tell between rich, but it would appear that the entire piston is clean. However rich can do this as well, but typically a rich condition will just slightly enlarge the silver areas near the ports.
 

·
Registered
Joined
·
648 Posts
Discussion Starter #4
Thanks 650,

I have a 2001 xc800sp that I just got and the stock jets are 460 mains and 45 pilot. This particular sled is jetted with 430 mains and 17.5 pilots and I'm trying to figure out why. I know why he changed the mains as the sled came from southern Minnesota, but I went back to 460's as I am in Manitoba and the weather here is much colder. Why would he change the pilots down that low and should I be concerned enough to go back to the stock jets? There are no other mods to the sled other then a boost bottle and clutch kit. I'd rather give up a 5% performance gain to become more reliable. Isn't most jetting jetting changes done on the mains only?

Thanks,
 
1 - 4 of 4 Posts
Top