#1986 250r atc stock carb install

I'm sure they put an aftermarket reed valve on the machine also, as well as a pipe, so inspect the reed petal ends for cracks or wear, and do a compression check, I can't tell you the magic number, but if its low they usually start hard, and down on power,( but you stated its running strong)and thats when they get down to around 100psi., and its time to rebuild. If it's fouling out at WOT regardless of how you run it then I would safely say your MJ is off, but it just could be worn parts not letting it transition correctly. If your easing it to WOT and its running clear it makes me think its not the MJ size, but something else causing your issue, but I may be wrong, as the MJ is flowing fuel at lower throttle settings than 3/4 to WOT from the needle setting, as the tapered end is letting fuel through, its just MJ only from there on up. Someone here that still has one should be able to tell you what their mixing their ratio at nowadays. When they were new it stated 20-1 on the tank, but that was with oils of the 80's.

#1986 250r atc stock carb install

I would install a fresh spark plug thats gapped correctly, and clean your air filter, and drain your fuel tank, check your fuel flow, and put in some fresh premix with a good quality fuel, and good two cycle oil, and mix it accordingly. I really think it has to do with carb wear, or being dirty somewhere, and/or needing rejetting. To the OP, you can measure the inside diameter of the intake side of your carb, not the air filter side, and find out what size it is. Good luck, and get that thing running right, as they are too much fun. Coming from alaska i would say it was jetted quite fat for the cold air, and the elevation changes would make it different also. If your choking out at high speed 3/4 and up it is the MJ being to large. If you do have the 38mm maybe you could contact CT, and see what jetting specs they recommend for a starting place for that set-up, and they might have a carb rebuild kit for it also.

I would double check the carb, and make sure what it is, and check for air leaks in the boots, and also check the reed valves for wear, and do a compression test just for maintenance sake. Heres the link to the CT site that shows what came with that kit, and the carb listed is a Keihin 38mm pwk carb. I bought the fourtrax 250r new back in 86 and it came stock with a 34mm keihin carb, so if your saying that 310 kit has a 48mm on it, (I'm not sure if they even made one of those)that has to be the issue as that is way to big for that set up.