1983 xr500

I have posted this problem many times before, and havent figured it out. when I start up my bike (xr500) with the choke on, it idles fine, but when you give it gas, itdoesnt rev all the way, and sputters and backfires, and does the same with the choke off, but when I cover the lid of the airbox completley, it revs great. I have cleaned and rejetted the carbs, with 133, and 108 main, and a 55 pilot. this has really been driving me crazy for months:banghead:

I think you're having a similar problem that I am having with my TT600.To start with my yamaha was blown up but still ran it passed alot of oil and would foul plug this is what I thought was my performace problem.Long story short overhauled it and it still ran like hell.Cleaned both carbs out a couple of timesstill ran like hell.What I found was that acouple of owners ago someone had raised the needles in the slides all the up and made it run so rich it wouldn't accelerate.It sounds to me that maybe a previous owner has lowered the needles in your carbs all the way down causing a severe lean condition.This would be why when you choke the air box down it runs better.I would look at the clip location in the needles bottom notch=rich top notch=lean.Any books that I have looked at don't show what the stock needle clip positions are hopefully someone else here posesses that info and maybe the clip positions for my TT600 also.Please help us.

I am not sure how to check the needles on it, as it is a dual carb. there are these little plates that you can take off on the top to check, but the whole pulling mechanism is on the side.

You should first find an appropriate schematic to show the disassembly of your carbs. I think the plate on the top of the carbs is just a cover. Under them you should see an internal linkage that actuates the slide/s. This internal linkage must be removed to access the slide and the needles. I remember a similar setup on an older XR I once worked on. You'll probably have to remove the carbs to service them.

You'll definetly have to remove and separate the carbs to do this as the throttle linkage and shaft needs to be removed from the carbs to get the slides out.Do you happen to know any of the history on the bike sometimes that could in the diagnosis.Was it parked for along time,was there a performance problem and some body messed with it and couldn't get it right?It would be interesting to know and also might shed some light on the problem.

well, I just got tipped that the stock main jet is actually a 135, so that could mean I need a bigger one than the 133 on there.

thats why i leave my carbs alone. They are working great as stock.

Your bike is way to lean. You need to rejet it.

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