Spent two days riding the logging roads in Montana at a resonable pace and suddenly the the machine acted like it was out of gas and tried to sputter and die. I nursed it back to elk camp and saw that I had a half tank of gas left. checked the plug and it was wet. I threw in another plug and still the same problem. Checked the air filter and could see sunshine through it. I checked the carb and noticed the idle screw was cranked all the way in. I fiddled with the idle screw and only could make it idle worse by unscrewing it. I tried to adjust the mixture screw, but it still was wetting the plug. Then I went for it and headed to the reeds, all were fine, and the rubber boot was fine also. I did notice some scoring on the intake side of the piston....that made my wallet cringe. I'm going to run a compression check to start and the try a mikuni rebuild. Am I missing something easy or am I on the right track? thanks

 

Your on the right track with doing the compression first. If the compression is ok then look at the float in the carb. See how high it is and if there is any burs on the pin. Also make sure all the holes are clear of debri. Especially the air bleeds.

 

can you check the level of the float while the carb. is still in the atv?? Can a week-end tinkerer handle a mikuni carb rebuild? I took the bowl off and wiggled the floats and gave it a week-end tinkerer (that has a full series of Time Life Books and a set of Craftsman tools) and couldn't see any thing that would give me an indication of something wrong. The manual says 1.5 turns and I turned it down all the way to 1/2 a turn and couldn't get the plug to dry up in my short little test runs.

 

DanaDog I have not rebuilt a Mikuni in years. They just don't need rebuilding. A cleaning, yes, but a full on rebuild, no. Most of the spec's for a carb that I have delt with call for the float leavel to be 90 degrees to the carb body when upside down.
As you look down the carb throat there should be some small holes around the throat. When you have the bowl off shoot some carb cleaner down these little holes. These are air bleeds and if they are clogged up the carb will go way rich.
The reason I say to do the compression first is because if you are down on compression the burn will be bad and it will make the plug look wet and black. Check it first and then mess with the carb.
If I had to guess I would say you have some crap in the air bleeds.
Let us know what you find.