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Message started by ThumperPaul on 01/18/26 at 07:58:21

Title: Air Fuel Mix Screw - Metering Air or Fuel
Post by ThumperPaul on 01/18/26 at 07:58:21

Does the AI Overview below contradict itself? Compare the 1st paragraph to 2nd paragraph. I think I agree with the first paragraph, but dang I’m confused. At least the adjustment procedure is the same either way - twerk it back and forth until you get the idle high and smooth. AI also should have mentioned setting the idle as low as possible when the procedure is performed.

Turning an air/fuel mixture screw clockwise makes the mixture leaner (less fuel/more air), while turning it counter-clockwise makes it richer (more fuel/less air); however, this applies to an "air screw" (metering air), and for a "fuel screw" (metering fuel), the effect is opposite, so always check its location (airbox side = air screw; engine side = fuel screw) or tip (blunt = air, pointy = fuel) to know for sure, with the general goal of finding the highest, smoothest RPM.

How to identify and adjust:
Identify the Screw: Look at the carburetor's location relative to the engine.
Air Screw (on airbox/filter side): Meters air. Clockwise (in) = richer (less air); Counter-clockwise (out) = leaner (more air).
Fuel Screw (on engine side/bottom):Meters fuel. Clockwise (in) = leaner (less fuel); Counter-clockwise (out) = richer (more fuel).
Tip: Air screws often have a blunt tip; fuel screws have a pointy tip.

Adjustment Steps (General):
Warm up the engine completely.
Gently turn the screw all the way in (clockwise) until lightly seated (don't overtighten) to find the baseline, then back it out to the factory setting (e.g., 1.5 turns).
Turn the screw in (clockwise) until the engine stumbles, then out (counter-clockwise) until it stumbles again.
Adjust to the midpoint between these two points for the highest, smoothest RPM.

Title: Re: Air Fuel Mix Screw - Metering Air or Fuel
Post by ThumperPaul on 01/18/26 at 08:03:26

Please tell me this is right?

If the mix screw is on the airbox side, clockwise is leaner.

If the mix screw is on the engine side, clockwise is richer.

Or do I have it bass ackwards?

Title: Re: Air Fuel Mix Screw - Metering Air or Fuel
Post by Fast 650 on 01/18/26 at 09:18:10

Easier way to visualize this is that if it is fuel screw, screwing it in chokes off the fuel flow and the mixture gets leaner.

If the screw is the air screw then screwing it in chokes off airflow and the mixture goes richer.