I have a 2001 Big Bear 400. When I got it, it had sat for a while and the carb was in bad shape. I thouroughly cleaned it, replaced the throttle diaphram (it was badly torn) replaced the spark plug, air filter, and the oil.

After doing all of this, the thing fired right up, and ran fine all day long. I parked it in the garage for the night, and it would not start the next morning. I thought maybe I had a little more gunk in the carb so I took it back off and cleaned it again. I put it back on and it started up. I thought "problem solved."

Well, it wasn't solved, and that seems to be where I am. I can run it after I take the carb apart and put it back together, and it runs fine, but after it sits for more than an hour or so, it won't start again. I know the spark is good, cause I can pull the plug and when I crank it, I get a strong blue spark.

When it wouldn't start, I would pull the plug, and it would be really black from carbon, not oil, and it would be wet with gas. I'm thinking it's getting too much gas. If I turn the petcock off and it sits for a few days it will start then as well.

What do I need to do to get it right? I question whether the choke is working right or not. It moves freely in and out when I have it apart, and the cable seems to be fine, but could it be binding or something?

If anyone has any suggestions, please let me know.

Thanks.

texretvet

 

did you take the entire carb apart and spray it out with carb and choke cleaner?

try adjusting the choke a little bit that could possibly be the problem.

Also the needles and floats might not be workings smoothly and letting to much gas in.

 

Thanks for the reply!

Yes, I took the carb all the way down, cleaned it with b-12, a brush and a small peice of wire, to get inside all of the jets and everything. Matter of fact, I ended up buying another carb on ebay. The carb I bought, it had the choke stuck in the main body, and the guy had chewed the body up some trying to get it out.
So, basically, I have replaced everything on the carb other than the main body and the choke piston thing. I still get the same problem. so the problem must lie within the choke or the main body, or the adjustments.

On a completely different note, I have seen quite a bit on here about valve adjustments. How would I know if I need to do this?

Thanks.

texretvet

 

buy a service manual and read the specs for the vavles and carb adjustments

 

Thanks, I will definatly get a manual. What manual do you guys recommend? I bought a clymer manual when I rebuilt my little Honda, but didn't really use it that much, considering it is a pretty simple machine compaired to a newer quad. I have seen a Haynes manual for the Big Bear, or should I look for an actual Yamaha service manual like they would use at the Yamaha shop?

Thanks,
texretvet

 

Is there a carb(other than the mikuni already on it) that I can just swap in on this Big Bear 400? Maybe a better carb would give me less problems.

Thanks.

 

i too was having same problems with my 2000 big bear i went over the rubber intake and air filter hoses and now it seems to run and start much better and plug not getting carboned

 

What do you mean by "went over the rubber intake and air filter hoses" Did you replace them, or clean them or what. I am still having problems with it.

Thanks

 

i cleaned them and put new clamps on and made sure everything was sealed tight while running sprayed carb cleaner all around carb to make sure there were no air leaks just had it out this weekend after it sat for 2 weeks and it fired right up and ran great

 

That may be my problem. I'm gonna get out in the shop this week and see if I can fix it. Hopefully I won't have this problem anymore.

Thanks.