My trusty old Yamaha Big Bear usually gets a lot of use, so I don't worry much about the gas going bad. Well, with all the rain, and me not hunting so much, it just sat idle for a while. I charged up the battery and fired up the ATV this morning. Fired up just fine, but will not idle. Dang it. My fault. I ran it up and down the road for a while, put some carb cleaner in the tank and ran it some more. I hoped that might just clean what must be a plugged idle jet, but no luck so far. I'll let it sit with the carb cleaner, and I'll run it some more, and hope.

I used to have that problem often with a Honda I used to have, but never had the issue with the Yamaha. So, I'm open for suggestions that will solve the problem without me having to pull the carb. Whaddayathink?

check your airbox... make sure you didn't have a mouse get in there and mess stuff up. other than that, get your small tools out and get ready to do some carb work.

FIL had a Kawasaki that had a similar issue after it sat for a while. I pulled carb apart and cleaned it and it ran fine for a day or so and started it again so I repeated the process and got the same result. Next time I noticed the fload was coming apart and little bits of it were plugging up the carb.

Pull the carb, pull the needle valve, the jet, the floats, and soak them in Chemtool over night. Next day blow with compressed air. A safety pin comes handy cleaning the needle valve. Reassemble and ride on

Slightly better news. I did check the air filter, and no problem there. And after I put the carb cleaner in there and ran it up and down the road, it will now at least idle without dying. Not what you'd call a smooth perfect idle, but I'll take it for now. I'm thinking that if I'm getting any fuel flow through the idle jet, the carb cleaner has to be getting to the problem area. Tomorrow I think I'll drain the tank and fill it with fresh gas and more carb cleaner and see what happens.

Worth mention is that several times in the past year, my pole saw barely ran. It was sputtering and missing and would not idle. Finally I just dumped out the gas and put fresh in there and it ran great then. Hopefully, that logic will work for the Yamaha.

Man, I don't want to have to pull the carb off. Cross your fingers for me.

I'd run a strong Seafoam/gas mix

Yep. See if you have a pure gas station near you, if not, get a couple cans of four stroke gas from one of the big box stores. Empty the tank, put that pure gas in with about a half a can of seafoam, and run it through. Then fill it with good gas and a little Sta-Bil in the blue formula.

In the future, if it's going to sit up for a while, the last time you run it turn the petcock off and let the engine run itself out of gas.

You may want to change the spark plug it may be starting to foul due to the bad gas.
Couldn't hurt.

I did clean the plug, which is pretty new. That did help, but I still have that rough idle. Just from the way it's acting, I'm sure the idle jet is my problem. I was gonna drain the tank this morning, but got sidetracked by the wife. She wanted some trees trimmed, and I had a really big oak limb on a fence. So, I wound up making firewood. Whew!

The Yamaha runs fine at road speed. It's just the idle that has recently gotten bad. The last thing I'll do, when and if forced to do it, is take the carb off. I'll try the sea foam and hope.

Seafoam and green stabil or lucas ethanol treatment....I always keep this in my gas cans and I do not have small engine issues....weed eaters, blowers, saws, mowers...dirtbikes. I don't know if it matters, but I only buy shell or chevron full for that stuff.

If it's running at idle, even rough, and doing fine at road speeds, you may need to adjust the idle. Turn the idle knob or screw, until the idle rises and smooths out. Get on the ATV and put it in first gear, if it lunges forward or moves in its own under power, then back the idle screw back down.

BigPig, I've had to speed up the idle to keep it running. Till recently the idle was real smooth and even. Then I let it sit. Wouldn't idle at all for a while after the long sit, until (I suppose), the carb cleaner opened up the idle jet a touch. Then the idle was slow and rough, which was not normal. I have sped it up, so it'll keep running at idle, but it's still rough. Like I've mentioned, I'm hoping that the carb cleaner will eventually soften up the partial plug of gunk in the idle jet. If not, I need to learn to love the rough uneven idle or pull that darn carb and clean the jet.

jmho
do it right and take off the carburetor
and clean it out properly. don't try to rig it
hoping it will get better. all you're doing
is sucking trash that much farther up in the
teeny passages and stopping it up harder
and it will be that much harder to clean
out when you finally have no choice other
than to take it off. i would suggest that in
the future you siphon off any old rotten gasoline
out and replace with fresh known good gasoline
any time this problem occurs. it's best all around
to keep fresh gasoline in any power equipment
or drain it completely dry during long term storage.

Seafoam and Lucas ethanol treatment are your friend.

I had a problem like that and found out that I had water in my gas tank. Try draining your tank and refill with new gas.

Hmmmm...I had not considered water to be the problem. The tank was low on gas for a good while. Could be condensation in the gas. I'll drain it a bit tomorrow and see what happens. Thanks.

Buy a carb kit from ebay for less than $20. Will come with all new parts and jets.

Our Mule was doing that at the start of this season, I ran it almost empty and filled it up with super unleaded and a full can of seafoam, before that tank was used, it was back to running perfect. This was after running it most of the season, (even changed the plugs, oil and air filter) and it was running ROUGH!

I drained the carb, and there was a small amount of water. Didn't seem to make much difference in the idle. Totally forgot to get the Seafoam when I was in town yesterday.

Still trying to avoid pulling the carb.

Just put some new gas in it. If the gas today sits for a few weeks, it's not going to run the way it should because of the crappy ethanol that's mixed in it.

If you are near ft worth area I could help you out. My experience is if the cleaner breaks some crude loose it will usually find its way into one of the jets or orfices. Sounds like you have crude in the idle jet.

I think I'll just give up and put a carb kit in it, or maybe a new carb. The carb is 16+ years old, so maybe it's time for a new one.

Pilot needle valve clogged. I fix our family 4 wheelers about every 6 months because of this. It's the ethanol. Pretty easy fix if you know how to take apart a carb.

I CAN do the carb, but I'm taking the old ATV to the Yamaha place this week (once the grandkids are gone) and I'll just have them fix the carb and adjust valves and whatever else needs work. About time it had a tune-up. Then, for Christmas, I've decided to get a new ATV. Why not...

It'll be a Yamaha Kodiak or Honda Rancher. It'll be red, and 4wd. Racks on front and rear. And a winch.

carb rebuild kit cost like $10