RPM's slow to idle ATV

[Mototrig]

Just rebuilt the yfz 450, it's the Carb version. After it warms up it's slow to come down to idle in neutral after I let off the throttle. Would that be a pilot jet adjustment to 1 step richer? I did the starting fluid spray all over looking for vacuum leaks and found none.

It starts fine and idles perfect. Just when I come off the RPM's it seems to hang for a few seconds.

Thanks

 

[outboard_256]

I would move on clip on the needle and see if it get's worse or better. If idling good then pilot jet should be ok. You also have an air or fuel mixture screw to help with the pilot jet if you think that's the cause.

 

[Mototrig]

I would move on clip on the needle and see if it get's worse or better. If idling good then pilot jet should be ok. You also have an air or fuel mixture screw to help with the pilot jet if you think that's the cause.

I've messed with the AF mixture screw and it's currently 3½ turns out. I'll adjust the needle.

Usually I can tune an MX carb but this one has me stumped. Thanks so much!!!

 

[outboard_256]

You can also pull the plug and take a look to see if rich or lean. But that only tells the story of the last rpm profile which is usually WFO so it may not be helpful at 1/4 throttle. You maybe lean at 1/4 throttle but ok on the main jet and your plug will look fine. I usually take note of clip position on the needle then move it up or down one and test ride. Then move it the other direction and test ride. It should get better in one direction and worse in the other. If it's worse both directions put it back to where it was. Also warm up your bike and make sure you have good gas when testing. I have run low on gas testing because you keep dumping a carb full of gas switching jets and don't realize it.

 

[Mototrig]

You can also pull the plug and take a look to see if rich or lean. But that only tells the story of the last rpm profile which is usually WFO so it may not be helpful at 1/4 throttle. You maybe lean at 1/4 throttle but ok on the main jet and your plug will look fine. I usually take note of clip position on the needle then move it up or down one and test ride. Then move it the other direction and test ride. It should get better in one direction and worse in the other. If it's worse both directions put it back to where it was. Also warm up your bike and make sure you have good gas when testing. I have run low on gas testing because you keep dumping a carb full of gas switching jets and don't realize it.

I haven't even cracked half throttle yet, it's a full rebuild. Crank, rod piston ECT. If I read the plug (which I'll do Friday) it'll only be colored from mostly quarter throttle. Judging by what you are saying I could be lean at 1/4 throttle which would be a needle adjustment richer.

 

[outboard_256]

I haven't even cracked half throttle yet, it's a full rebuild. Crank, rod piston ECT. If I read the plug (which I'll do Friday) it'll only be colored from mostly quarter throttle. Judging by what you are saying I could be lean at 1/4 throttle which would be a needle adjustment richer.

Ya I would pull the plug then. White ashy color is lean, black oily is rich. Coffee/tan colored is good. Now when moving the clip on the need you have to really think about it. Moving the clip "up" actually drops the needle making it leaner. Many people get it backwards. That's why earlier I suggested moving it both ways and going by feel as it covers both bases so you can't get mixed up. Does your carb have an acceleration pump? Have you checked to make sure that's working properly. That just popped into my head, if it's not working it could also create a stumble.