A friend of mine has an older (don't know year, it's yellow) 400 sport 2wd. Anybody have a recommendation to start with to rejet to 5000 foot minimum altitude? The thing seriously bogs at low RPM, and barely runs when it is in the mountains. I am a snowmobiler, I know the clutching and how to jet, but I would like to know if anybody has a recommended starting place for jet size. Also, I haven't torn it apart, what carb does it have? A Mikuni round slide? Thanks for any help.

 

Yes, a 34mm roundslide. I cant help you on the jetting because I am at 900ft. I would think a 200-220 range on the main, but maybe someone else will chime in.Bubba

 

Hi I am at 4800 ft plus and running 190 main works great but add mods like I have and better be jetting up

 

you're kidding? the stock jetting with the 34mm carb is 230 main,at this
elevation it should be safer to start at 270-280,also the pilot jet must be increased at that altitude too or you'll have always this bogs down low without pulling the trigger at idle...

 

I think you are backwards scramblered. I don't think it would run at 5000+ with 270-280s if it comes stock with a 230. It's already too rich with stock jetting.

Thanks for the recommendation Jwb, I actually have some jets around 200's for my Indy 500 sled, so I will be good to start with. Then it is tinker tinker tinker... :-) That's half the fun of owning machines, playing with them to make them run better. Of course, my wife doesn't think so, but that's a different story. Thanks again.

 

I would start 2 sizes lower than the factory, maybe a 210. The higher the altitude the lower you have to jet.. Less air = less gas. Same with wintertime, colder air = more gas. You should also think about changing the weights if you go above 6000 ft. You would need s53g weights in that case.