Hey all,

New here, and looking for some help if possible. I got a 98 Big Bear 350 a couple weeks ago with a leaky needle valve. It also bogged a bit as you ran through the gears so I figured The carb could use a good clean. I bought a new Needle valve and Seat, replaced them and cleaned the carb, put it back on the bike and it now starts up and idles fine, but when given gas it just bogs down, won't rev up, and has no power.

I've cleaned the Carb 2 more times, taking out every jet, soaking everything in carb cleaner, and still the same problem. I replaced the spark plug, ran it with and without the air box cover, checked float height and believe I have narrowed it down to the Diaphragm not lifting the throttle piston. When lifting the piston manually, it seems to be back firing into the carb. I checked the diaphragm and there doesn't seem to be any rips.

I'm pretty stumped at this point, gonna take the carb into a mechanic at work Monday if I have no luck over the weekend, but any suggestions as to what I could try or look at in the meantime would be greatly appreciated.

Thanks in Advance!!

 

I would take the cv slide gate out[the plastic gate thats has the temper screw heads]. but be real careful an not break the heads off. i heat up the side of carb were the srcew goes thru But becareful for gas fumes and dont take much and make sure the carb is clean from gas fumes , they are orings around the gate but thats is another problem yamaha don,t offer them i use an honda blue orings work great, bad or flat orings causes excess fuel around jet holder and cause rich mixture which causes an bogg. just my experince..Good Luck....

 

My Clymer book says you should NOT use carburetor cleaner around plastic and rubber parts, For your information only
I gave up on mine looking for a new / rebuilt carb same 1998 Big Bear YFM350FWBK any body got one?