I currently own a 2005 360 prairie, this thing is running WAY rich I have jetted the main all the way down to a 142 (stock is a 155), re-set the valve lash and of course cleared the pilot jet. It runs ok when it is cold and with a new plug in it but once it warms up it will idle fine but sputters when you try to throttle it and if it will allow you to rev it to a 1/2 to 3/4 throttle it sputters. air filter is clean, choke is working (engine runs differently when choked) still turns the spark plug jet black and sooty. Nothing changes when the air filter is off and the diaphram is in perfect shape as best as I can tell. Im at witts end with this thing. Any help at all will be greatly apreciated.

 

my 2006 prairie 360 had the same sputtering problem when taking off from an idle while it was hot. only happened when the bike got really hot. I thought it was vapor lock for a minute because of that. I finally got the valves adjusted because there is a known issue with the exhaust valves and that 'almost' completely cured my problem. it still wants to sputter at about 1/2 to 3/4 throttle, but that's with no load on it. it's fine at those rpm's on the trails with a load. once in a great while it will sputter taking off from an idle when it's hot. I would suggest checking the valves again. you did rejet so that's one difference from mine. but the fact that it runs fine when it's cold tells me it's not a mixture issue. if your mixture was off that much you'd know it when the engine was hot or cold. with the stock jet you should be right on with your screw about 2 1/2 turns out from all the way in. that was the case with mine before and after snorkeling. please let me know if you find something out.

 

oh, two more things. I could spray the carb with cold water and it stopped sputtering, and with the airbox lid off it corrected the problem too. don't know if you tried it with the lid off. that also made me think the mixture was off. but it was the valves for sure.

 

Set the carb setting back to the original factory spec. There are gizzilion P360s out there with the same carb setting and they run perfect.

Two possibilities to check:
> The choke mechanism on your 360 is actually a fuel enrichener with a little plunger that opens and closes. If it becomes sticky because of corrosion or gummy fuel, it can hang up partially open even when choke lever is at OFF position and extra fuel could be flowing into carb making the engine run rich.
> Set the valve clearance to the looser side of the spec or right at the maximum loose/large side. If the valve is too tight, not enough fresh air can come into the cylinder and the end result is the same - too rich.