Carb adjustment screw location 400 yamaha big bear

Question edited for clarity and add maker.
Question moved to a Big Bear category.
Chat GPT4 Answer from AI Bot 'Gerry' deleted.

Mikuni tuning in the link. The screw is under the intake bell.

https://www.google.com/search?q=mikuni+bsr33+carburetor+tuning

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limited info generic answer usually if carb floats dont shut or valve leaks fuel will leak into piston cylinder down into oil https://www.autopartsrepairs.com/yamaha-big-bear-repair-manual-250-350-400/

Sounds to me like your not getting enough fuel change fuel filter and tak gas out of tank and clean it out a few times as the screen in the tank may be clogged also if you have an electronic fuel pump make sure it is working properly

http://www.partzilla.com/parts/search/Yamaha/ATV/1998/BIG+BEAR+4WD+-+YFM350FWBKC/CARBURETOR/parts.html this page shows the carb all pieces including air mixture pilot and main jets

idle control is sticking need carb adjusted or float maybe

sounds like your mixture was leaned out because ur filter was cloged up ...making it run rich so was adjusted by screwing air screw out, now uv cleaned it, adjust it to make mixture richer by screwing back in until runs smotherly

If it's been sitting around for a while it could be the idle jet has a little craip in it (it don't take much) but if it's spitting fuel out then I would make sure the float levels aren't sticking.

I'd clean and adjust your carb/air filter. it probably running too rich and fouling the plug.

Sounds like the carb could use a cleaning and setting by a professional...install a new plug and a new air filter.. AFTER the professional carb cleaning and setting.,,do this and repost

That sounds like it is running too lean. You may need some carb adjustments to account for your altitude.