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Hi all,
I have my jetting adjusted just right but the bike runs extremely rich in idle even with the idle screw turned all the way in. This causes me to stall in races where i'd rather not. With this limited information could anyone point me in a direction towards a fix?

Carb is set like so:
Main - 145
Pilot - 42
Needle - R1173L
Clip - 3rd
Air Screw - 1.5 out when its colder, 2.0 when its hotter

This could be as simple of a fix as replacing the jet block gasket in the carb. I'd start there.

Do a "jet block gasket" search on here for more info, I see this come up fairly often.

The idle screw raises the slide and if you have it screwed all the way in the bike would be screaming. It has nothing to do with rich or lean. The air screw controls the amount of air entering the idle circuit. Maybe you need to clean the idle circuit passages or the idle jet. If you do have that idle screw in all the way and the bike isn't idling way high!!! Then you have other problems, you need to go thru the basics.

Agreed. The idle screw shouldn't affect rich or lean, just idle speed by moving the slide. I'd suggest starting from scratch.

Thank you for the replies all. I realize I made a mistake when I associated the bike running rich with the idle screw adjustment. The bike runs fine if I turn the air screw out but it still struggles in idle where it stalls when the clutch is in for a few seconds.

I have ordered the jet block gasket from jets-r-us part #1202-834-2000 (SKU 021-532) for $4.41.

Since the bike is old I figured it would be safe to purchase their Carburetor rebuild kit PWK33 - 41mm 020-110 $40.95.

I will give an update once it is installed.

Update:
No for sure way to know what was wrong because I didn't just replace the jet block gasket, I also replaced the rest of the carburetor gaskets. All existing gaskets looked fine but I replaced them with new anyway. On top of that I also hit a tree stump, exhaust pipe first, which changed the pipe's geometry and lost the perfect seal between the pipe and the engine. So I am also changing the exhaust pipe. And...while replacing the gaskets and cleaning the carburetor I realized my throttle cable was too tight and my slide was raised about 5mm.

I will not be able to test the bike until I receive the pipe on Sunday. I will update once I receive.

On a side note, you could send out that damaged pipe for repair. I recently sent my FMF Desert pipe to Pacific Crest Pipe Repair to get the dents out. It came back looking absolutely amazing! It looks brand new again. It never hurts to have an extra pipe around just in case. Besides, it's kind 'a fun to switch back and forth between Woods and Desert pipes depending on where I am riding.

I put on a new pipe and cleaned the carburetor with new gaskets, including jet block gasket. It still runs rich. I'm going to clean the air filter to make sure that has nothing to do with it. Then the next step will be to look at the reeds.

turning the idle air screw in makes the mixture richer, not leaner

Jaguar wrote:turning the idle air screw in makes the mixture richer, not leaner

Am I wrong to think that turning the idle screw increases the air/fuel mixture and not just more fuel? Slide raises allowing more air and needle raises allowing more fuel, exactly like twisting the throttle?

Willbilly wrote:I put on a new pipe and cleaned the carburetor with new gaskets, including jet block gasket. It still runs rich. I'm going to clean the air filter to make sure that has nothing to do with it. Then the next step will be to look at the reeds.

Reeds look fine. I cleaned the reed valve and reeds, and boot between reed valve and carb and reinstalled. Will check back with air filter this evening.

I hit the spot last night. Everything works great. Clean air filter/ rebuilt and cleaned carb / cleaned reeds and reed valve / fmf gnarly pipe.

145 main
40 pilot
3rd clip
2.0 out

Yes turning the idle adjustment screw clockwise or in raises the throttle slide just like if you turn the throttle only a much finer adjustment then trying to use throttle adjustment. The air screw when turned clockwise decreases the amount of air in the circuit making the idle richer and turning it out gives more air leaning the idle mixture. I have a kx 420 1980 I believe that came from the factory with no idle adjustment you have to use the throttle to keep it running let off and it dies.