Hello,
I have a 1998 big bear 350. It cranks fine and will idle fine "for the first few mins" then when it heats up the air/fuel ratio seems to richen. It will run like a beast for the first 5 to 10 mins of operation but after a while it runs like crap. It looses all torque. Then eventually if you give it more then 3/4 throttle it will load up and act like it floods out. When I first got it if I took it down a steep decline it would flood out. But i checked the float and it wasn't sticking or cracked. I've cleaned the carb a million times and finally jetted the main jet to a 122.5 instead of 125 stock since the spark plug had a lot of carbon build up. I've done nothing to the pilot jet since it idles fine even when it has no torque. It's the same with the needle jet. When it's running terrible and I am revving it up in neutral it only starts missing about 3/4 throttle and up. Also most of the time I cut it off it backfires really bad. I think that unburnt gas is building up in the exhaust then igniting. For some reason im beginning to think its not the carb. I've changed the spark plug to what was in it when I got it which is a NGK d7ea. The oem plug it calls for is a d8ea and i've tried that as well. All of them read rich. I've checked the valves and they are adjusted right. I believe the lash adjustments are the same as a warrior and are intake .002-.004in and exhaust .006-.008in. The only mod I have on it is a snorkel kit. This couldn't effect air/fuel ratio this bad could it if so I already jetted the main jet leaner so that would have to fix it unless i didn't go low enough tho doubtful. The only thing i haven't done is a compression test but I used to race a 2001 YZ450F and i remember the compression on that bad boy. Although it was a kick start my Big Bear seems like its got the right amount of pressure when i had to pull start it for a month due to a faulty battery. Please Help!!!! Thanks...

 

almost seems like the fuel bowl height is wrong, or maybe bad valve seats.

 

well the float is none adjustable so how would the height ever change if the carb is still in stock location and when i checked the valves the seats were not worn.

 

I say they were not worn because the valves didn't need adjusting. If one of them was wore then that valve would need adjusting correct?

 

i dont know anything about 4 wheelers but im having same prob i do know if u take breather hose off and manually lift the slide it fixes it cant figure why its not getting enough pressure to lift it on its own

 

Float could have a hole in it, taking on the weight of fuel,.... allowing too much fuel flow,.... flooding. Once this occurs, sometimes you get a lot of "backfiring". which is actually Afterfiring,.... fuel in the exhaust, which lights up and explodes once it hits that "hot spot" in the exhaust..... Just an example.

 

took my carb off had it checked they said there no reason it shouldnt work told me to make sure the air filter box was on good and tight and to make sure the breather hose wasnt cracked or stopped up

 

Its adjustable, you just bend the tab were the needle valve rests.

 

I have a 1992 Big Bear 350, it's doing the same thing with a brand new carb on it. Still no idea why

 

Probably bad or worn gaskets/seals, this is why just cleaning old carbs never works. A good quality rebuild kit should be used, so all adjustments can be set to factory specs including the float. Valve seals being worn has nothing to do with adjustment, worn seals or guides regard the stem dia and the hole they go into. Whether compression feels good or not, a compression test will give real needed information. Stop guessing and make real accurate tests and rebuilds to get good results. Cutting corners rarely works well.