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carburation! on a 2 stroke??

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well this is about an 03 yz 250. we jetted my buddys bike for the winter, -5 - -20 degrees celcius. so far everything is stock. except the main jet and needle setting. went from a 175 main to a 180, still lean. went to a 185, still lean. went to a 190 and raised the needle one clip, still lean. went to a 195, still lean. now after every hard ride ive checked the plug. and the porcelin part is white, new plug every time. from what i was told, to jet a bike for the winter you should only need to change the main 1 or 2 sizes, so from a 175 to a 178 or 180, and maybe raise the needle one notch. now ive changed the main 13 sizes and raised the needle one clip and the plug is still white. does this mean there could possibily be an air leak on the intake side. im pretty stumped on what to do next. we were gonna try messen with the air screw. out for more air(lean), in for less(rich), does that make sence? he did the crash the bike pretty hard last time he rode it, summer about 3 or 4 months ago.

thanks for any help

shane

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Are you running stock compression, have you had the head modified? make sure the carb is seated in the rubber boots and well sealed. Is the air filter sealed against the airbox? I would not touch the air screw. I used to go up 5 sizes on the main on my ATC with a Mikuni carb (which may not equal the same thing as going 5 sizes up on the carb your running) and one notch richer on the needle then change the head gasket back to stock from the thinner CR style head gasket that I ran in the summer, also I richened the fuel mixture from 32 to 1 to 24 to 1 and only ran synthetic oil in the summer. If your not running the airbox lid or have holes in the airbox you may want to run the lid or seal the holes, also its hard to get a good read on a brand new plug I used to putz around a bit on a new plug just to get some color on it then go wide open back and forth a couple times and shut off right away so I could get a good read on the main. Maybe someone can be more model specific for you but this was my procedure, I hope this helps. Be patient you should only have to do this once and remember plugs are cheaper than a top end. I'm not sure you moved that many sizes on the main does anyone know how the jets jump with these numbers (Keihin?) do they go by 3's 5's or what. Good luck. :)

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oh shit..sorry i screwed up...i didn't change the main 13 sizes. i change them 8 sizes. i owe a yz so i positive they go like this, 175 178 180 182 185 188 190 192 195. i was doin it in my head before i think i was high, so kids don't smoke cheeba, this was an example of what it can do. i did notice that after the last ride he has a large crack in his pipe, about 60 inches from the cylinder. the was a minute crack there before that i saw but it is now about 20 times the size. thanks

shane

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i know this is a dumb question, but are you riding on the main jet? richening the main won't help if most of your riding isn't WFO

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haha damn i screwed up that last post too. but anyway, yes about 85% is wide open. were i live theres a few diff. large rivers so were on those wuite a bit. and at this time of year the trails are real smooth, no mud obviously, so you can go wide open everywhere. im not to sure how he rides his own bike but when i test rode it for a day i was pinned everywhere, on and off, i wanted to get a good reading so i rode it pretty hard. im starten to think hid exhasut leak is pasrt of the prob. my 400 is jetted almost spot on but leaks where the header and the pipe join, im pretty sure thats whats making my plug white.

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