Hey y'all, I have a 2000 Bear tracker 250 2WD that has me stumped. I replaced the intake manifold/boot, the carb is brand new and so is the air filter. All parts are OEM and properly installed to spec (I've double and triple checked). For some reason it will only idle/run when choke/partially choked. It responds to throttle while the choke is pulled, but when I press it in the RPMs drop down like it's going to idle, then dies a second or two later. I can turn it over and start it with the choke off but again it dies very quickly. If I try to give it throttle with no choke there is no response and it dies immediately. I've tried adjusting the air/fuel screw from the recommended 2 1/2 turns out and all the way till it seats or falls out with almost no change whatsoever. I have even checked the timing and there is plenty of tensioner spring left, and all components look great.

Any help is greatly appreciated. I bought this for my wife and it is the only thing keep our family from going on a trip

UPDATE I drained the gas and put in fresh gas. Changed out the fuel line and went with a straight line vs having the filter and now it runs like a top when half choked. Still dies with zero choke but is somewhat responsive to the throttle now. Now do I mess with the air fuel mixture?

UPDATE #2: I double and triple checked the manifold and air intake hoses, made sure the entire air circuit was buttoned up. Toyed around with the Fuel/air mixture screw (around 2-3 full turns out from seated) and got it running fairly well. Rode it up and down the street fine but if I try to go wide open it dies right down. I could ride it all day long as long as I only use about half to 3/4 throttle. I jacked it up and popped it into gear to see if i could play with the fuel mixture to try and fix it, but i noticed when it is pinned and starts to die I can see a small bit of exhaust coming out of the air box hose. I'm going to try and adjust the valves tomorrow in a last ditch effort to fix this thing.

Video preview:
Thanks!

 

Set the idle speed (throttle stop) before messing with fuel/air settings.

Interesting story about a Bear Tracker, owner sent it to us to "get running" after a long lay up. Carb full of gunge so cleaned it, and tank, out but noticed slow running needle was missing, you could see straight up the hole into bore of carb. Because of the corrosion I could tell it had been missing for years so I thought, well it isn't going to idle but lets see if it starts now the main jet is clean. Tried it, not only did it run with throttle open, but idled perfectly.

 

wow ! That is crazy
i am getting ready to rebuild my mikuni carb because the cheap china replacement carb was having the SAME issues brand new...only ran with choke on.

 

Er, in your first post you wrote "the carb is brand new and so is the air filter. All parts are OEM." Chinese carbs are not OEM, so will need altering to suit your engine, main jet needle in a different groove, (if possible), may even need different main jet etc. Give the Mikuni's jets, and the holes they came from, a good blow out with compressed air and see if that works.