well i got my uncles 1999 sport 400 it has violet / brown clutch springs k and n filter an after market exhuast he didnt know what name it was but it looks like rcr so it prob is...well anyhow the prob is i just got it and just riding around town it goes great at full throttle but like after i go for a lil bit then let go of the gas and hit it again it just feels like its complete going to bog out it does it for like 5 seconds the quits....so i looked at what jet was in it and it was a 220 isnt that way to low and the air screw was set at 2 1/2 so iwhat i am asking is what main jet i should put in it what clip on the needle and how many turns out the air screw should be.....im also around 2500 feet above sea level

 

its seems a little low for a piped machine..i think i was running a 250 when mine was piped..

 

That has to be to small of a jet. I think mine came out stock with a 230. I think I would start with a 250 jet. And maybe the clip in the middle. Not for sure on the clip though. Just make sure you keep doing a plug check to make sure.

 

that 400 need special compression check,before going any further
you need at least 270 main jet with a pipe and silencer,air screw depend
on what pilot jet you have in it.you're lucky that engine haven't blown
yet.

 

With the stock carb I'm running a 250 on my wifes bike and I'm at around that elevation. It runs real strong with that jet. It sounds like you could be starving for fuel. Check all of your vent lines as well. Also be sure to check the plug for color.

 

well i just got this quad sat night and today i was out riding around town seeing whats its doing and well it did what i said but as soon as u put the choke on it stops the let the choke back out and it goes again.....then i was out on a straight stretch and it just dies on me and when i went to pull start it it was like kinda griding so my friend riding my quad pulled me home and i toke off the top end and checked it out it looks like its running very lean and the spark plug was white...so i wnet to pull start it again and it stoped making that noise so i toke off the air box and theres like a 1 inch hole cut in it and i toke it for a ride without the air box on and it ran great really strong......so im going to go get a main jet for it this week some time should i get a 270 and a 250 and see which one works better? and what was causing that griding noise??

 

Not too sure about that grinding sound. It could have seized on you on that long stretch if it was running lean. You got lucky if it did since it unseized.By what you're saying it sounds like when you're having the problem and you engage the choke it goes away? If that is the case then it sounds text book lean. I think that a 270 would be too big of a jet. Try the 250. It's 30 points bigger than what you have right now. If the plug was a greyish color than that means you are burning(melting) the top of the piston and won't be long until there's a hole. Put in a new plug and run it with the 250 on wide open throttle for a 1/4 mile stretch and then kill the motor with it at that postition(WOT) and then check the plug. If you have some color on it (light tan) then you're really close. The needle should be in the third position (Middle). Hope this helps.

 

that helps out alot...thanks ill tell u how this stuff goes after i work on it sometime this week