hey. I am working on a 2003 Yamaha big bear 400 4x4. and I am trying to ride it and I am pressing the lever. and I only got 1/4 of the way pressed and it boggs out. but if I turn the choke lever all the way turned to full choke and it accelerates just fine. please help I really want to go riding. and I could use any help I can get. any help is appreciated. thanks andrew

 

Welcome to the forums.
I'd start with a good carb cleaning.
After that, I see most advise to check the valve clearance.

 

ok, yeah I just cleaned the plugs, got a new air filter, new liquids in it, new plug, I noticed when I pulled out the old plug after it was bogging out when I went to gas up, the plug had carbon deposits on it and completely black, not even a little wet. and thanks for the help bud. I will try looking at the valve play and I will get back to you. I will keep u updated thanks so far bud.

 

Being black means a rich condition, having to run with the choke on means a lean condition. Either way the carb needs a thorough rebuild with a quality rebuild kit and ser to proper specs. If your engine quits running when the fuel tank is empty...you dont try rebuilding the engine before you decide to fill the tank. Due to age the carb rebuild should have been first...

 

I did rebuild the carb bud. I put an all ***** carb rebuild kit. I tore it down completely, and threw it in the ultrasonic cleaner, blasted all the passages out , and dryed it and put the rebuild kit in, adjusted it to 2 3/4 turns out like the said manual said. so I did bud, I will never lie on one of these forumns. I speak from the heart. bud. so I will adjust the valves and let you know.

 

Are you using the original airbox? Many times guys open up the airbox to let more air in thinking better performance but if carb not jetted to match the added air flow they will bog on acceleration. Seen some guys do a rebuild and try it out without the airbox on and find it bogging, only to install the airbox and have it run fine. We are just making suggestions here based on what you tell us.

 

yep everythings original bud. I will be adjusting it on Wednesday.

 

hey bud, whats the intake and exhaust valve lash I cannot find that anywhere. I looked on my atv, in my owners manual, and in my service manual. much appreciated thanks.

 

Yamahas are notorious for cracked inlet manifolds, so check it isn't that. Valve clearances will be listed in the service manual somewhere, I seem to remember most of the 350s were 0.003" for both valves so I guess the 400 will be similar.

 

If you cleaned the carb did you get the jets back into the right spots? I didn't one time and my big bear did the same thing yours is doing flip flop the 2 jets and bet your good to go.