I am having some issues with my 1995 yamaha timberwolf 250 2wd. When I first start my atv no matter if the weather is hot or cold I do not need to use the choke...and it starts right up. But the idle is very inconsistent. Without me touching the throttle the RPMS are going UP and down on there own and there is no rhythm.

If I choose to ignore this problem and ride around for a while the issue goes away when I am in gear but when I put it back into neutral the erratic RPM changes come back.

The only thing I can think of that may be associated with this is that when I put the atv in gear the atv moves a little bit on its own so I'm not sure if that means it can't idle when it isn't under load?

Where should I look first? It is one of those semi auto atvs.

 

Check the air intake plastic for cracks and leaks, make sure all intake clamps are tight. I would put a little Permatex #2 around all gaskets and seals, in addition to the air filter gasket.

It should create a non-hardening seal between the metal / plastic.

 

Thank you for the reply. I'm wondering why a crack or leak in the air intake would cause it to only do this when it is in gear?

 

I agree with heftylefty it does sound like an air leak. You can try spraying carb mating surfaces with carb cleaner or wd40. Just be careful with these products with a hot engine. If the rpms level off while doing this then that's the problem.

 

I cleaned out the airbox and put a new filter in. I checked it for cracks and didn't find any. I checked both air ducts and they didn't have any cracks or damage. I put a semi drying instant gasket maker on the seams and tightened the hose clamps down good and no change it still won't idle worth crap. If I give it gas it sounds fine but then it dies down and sometimes will just shut off because it is so inconsistent.

I took the carb off and cleaned everything and when I put it back together it idled perfect but after riding it for an hour it was back to the same thing.

Anyone have suggestions on where to go from here? Could it be the idle adjustment screw or the main mixture screw? I have tried screwing around with the idle screw and I can't make out ANY change at all if i screw it all the way in or back it off a bunch of turns.

 

If this carb has an enrichener take the plunger out and clean it and the bore REALLY well.

 

You said that it idled perfect after cleaning the carb before it started happening again and that adjusting idle had no affect on the idle. It sounds like possible debris in the fuel tank is making it's way back to the carb. I would clean from the tank to the carb.

 

I'm not sure if it has an enricher. It is a Mikuni carb. How do I go about cleaning the gas tank? Just remove it and rinse it out then let air dry?

 

Also not sure if it matters but white smoke comes out of the exhaust when it is in the dieing/idling stage. No smoke at all when I'm riding though.

 

Where is your mixture screw setting at now? should be at or around 2 1\2 turns . then adjust fine tune after bout 10 minutes of running. where is your needle jet setting[ that the long brass needle] thats moves up and down when throttle is used. [stock setting 3rd groove from top.] if every thing is set like this and carb is super duper clean then set the c-clip on needle down one to richen up that circuit you having problem with.IMO and try let us know...Good Luck.