Hey guys. I have had my 2000 Big Bear 400 4x4 for a few months now. I bought it basically not running and was able to get it running great with a good carb cleaning and adjustment except that it has a somewhat unstable idle and it has to be warmed up a lot in the winter before it will idle without the choke on. I have cleaned everything I can in the carb that I am aware of that should need cleaning, but I feel like I have to be missing something here... I dont think my Big Bear should be so hard to keep running without the choke on when its cold. I can understand a couple minutes of choke, but adter that it should be good to idle on its own I would think.

Is the Pilot jet and pilot screw the only things that should matter as far as the idle goes? Somewhere my idle circuit has to be clogged slightly. Factory settings on the pilot screw should be 2-2.5 turns out from what I have seen. Mine has to be at 6 turns out before it is rich enough to idle decent which tells me there is a problem. Just wondering if anyone has had any experience with the idle circuit on these carbs and knows something I may have missed..

Also, when I first got the ATV I had to move the main needle clip to the bottom of the needle to raise it up some. Seems like it should be able to be in the middle, but again, I have cleaned everything I can get at to the best of my knowledge. #18 in this diagram has me somewhat stumped though. Where is it located? The carb inlet?

2000 Yamaha Big Bear 400 4WD YFM400FM Parts, 2000 Yamaha Big Bear 400 4WD YFM400FM OEM Parts - BikeBandit.com

Thanks for any help!

Eric

 

Air bleed screw,,inside the air intake of carb, in the throat.

 

You mean that is what #18 is? It says main jet. I guess main air jet? And what exactly is an air jet for?

Im assuming I must have a passage still clogged since my jets are clean and I cant find anything else clogged. Although, I shot carb cleaner through all the passages the first time i had it apart. Maybe it didnt get some of the crud out. May have to soak it...

 

Had a user tell me to clean the idle jet. It's the smaller one in front of the main jet. I told him I did already any it didn't help. He told me to do it again. I did and all was well. I could run a small price of wire through it the first time I cleaned it. The second time I found if was still partially clogged. The passage really opened up when the scrap broke free the second time around. Made all the difference.

 

I usally disassemble the complete carb an dip it in an vatt. then inspect all passage way..Yes the air bled is the main air jet for carb to run but rearely get clogged there were it is.

 

Ok guy, I have made some progress, and although I think im going to have to pull the carb one more time, I think I may have it figured out.

Like I said before, I had to have my pilot screw 6 turns out just to get it to run rich enough to not bog. I had cleaned the carb before, but not with compressed air. So this time I shot air and carb cleaner through every hole I could find on the carb. Everything seems to be flowing well now. I got the ATV back together and noticed a difference immediately. It starts great and dont need to choke it all the time now, but now it is running rich. I have adjusted the pilot screw all the way in basically and its still on the rich side and if I open my idle enough to where it wants to keep idling and not sputter and die, it wants to have a hanging idle.

After some research over the past couple days, Im 99% sure my float height must not be right. I think it is allowing too much fuel to come in and flood the engine at idle. Im going to try and readjust it tomorrow and give it another shot.

So obviously before I had a clogged idle circuit causing it to be lean, but once I got it cleared, then the float height issue it had been masking was apparent. I will keep you guys posted but I think this will fix my issue. Thanks for the help.

Eric

 

dont forget you moved main jet needle up allowing for more fuel, a little easier to change first, though may not effect idle circuit

 

I need some help with my carb also. It start fine but when I give it full throttle it starts to sput and sputter. Also it smokes some and it smells like gas. And I looked at the air filrer box and there's and its wet from gas. Well I think it is because it smells like it.

 

Sounds like your float needle is not sealing correctly. The new gas is really bad for eating up the seats and rubber needle tips. Id replace the seat and needle and check your float height, reassemble and then go from there.