big bear trouble

i have a big bear that will only run with the choke on and about 1/2 throttle it wants to cut out and die but if i take the choke off it wont run at all. idles perfect. is it a carb issue or something like the cdi? ive had the carb apart a couple times cleaning it but it doesnt seem to help. the slide doesnt open as well as i would like almost like there is a vacuum leak somewhere. it was sitting for a couple years before i got ahold of it with gas in the carb. any ideas? im not use to the mikuni carbs

Jason,

I feel your pain man. I have a 2001 Big Bear that all of the sudden started acting exactly the way you are describing yours. The thing never gave me a lick of trouble, then all at once started running like crap. I grew up working on motors and quickly narrowed it down to a fuel related problem. So.. I tore the carb out, soaked it in carb cleaner over night, drained the entire fuel system, put it all back together, and put in fresh gas. Only to find no improvement in performance. I repeated the process... thinking I must have missed something. Only this time I decided to put new jets in (standard sized not a kit) just incase. Put it all back together... and still no luck. At this point I became rather frustrated and decided to tear the carb out for a third time. This time I ordered a Jet kit from Dynomax hoping to just richen the mixture a little. But while I was waiting for the kit to get delivered, I ran the carb through an ultrasonic cleaner. Since the kit still hadn't shown up, so I put it all back together. The wheeler now runs like new! Seriously, it hasn't run this good since I bought it new back in '01. I didn't even have to put the $70 jet kit in (which is now laying on my work bench BTW). My next project is my brother in-laws 2002 Big Bear with the exact same problem.

I have repeated this process with numerous small engines, from weedeaters, to snowmobiles, with great success each time. In your case since it has been sitting for so long without running, a good soaking might do the trick. But my advice is to find a shop with an ultrasonic cleaner and give that a go.

The problem all comes down to the gas. Small engines were not meant to run on enthanol. The new fuels with 10% or more ethanol only have about a 30 day shelf life before it starts to break down, so I suggest you don't use it on any small engines. As the fuel breaks down, it starts to build up a layer of "varnish" if you will that restricts movement and flow.

Good luck,
Kory

A note to anyone else reading this: Just trust me on this and do not run fuel with ETHANOL in any small engine application. You might get by for a year (maybe two at the most) before you have to have carb work done. Pay a little extra and find a gas station that sells premium fuel with no ethanol added.

Jason,

Oh and one more thing...

Just an observation, but I'll bet if you start the wheeler the way it is right now and keep it running for a couple minutes, the exhaust manifold will start to glow red hot. This means it is running too lean.

Kory

Quote:

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Originally posted by foxman_87
Jason,


A note to anyone else reading this: Just trust me on this and do not run fuel with ETHANOL in any small engine application. You might get by for a year (maybe two at the most) before you have to have carb work done. Pay a little extra and find a gas station that sells premium fuel with no ethanol added.

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+1 listen to this guy, he is right!

I had a boat motor same way. What causes this is the gas being used? high sugar content. Some say water content. How does water clogg jets and such in a carb. Its sugar. One thing that helps but is not 100 percent proven to clear up the issue is green marine stabil in every tank of gas.

On mine that was happening and had the carb gone over. It still ran that way so the guy figured out it was the cable that was no good.