Carb issue

ascory · Sep 20, 2019

I have a 1950 8 n and idle goes up and down what should fuel and air mixture screws be set at?

Steve@Advance · Sep 20, 2019

The idle mixture screw should be about 2 turns off the seat.

The main screw mix won't cause idle surge, so if it's running good under power, don't change the high speed.

The idle screw is only effective at very slow idle. It needs to be down around 400-500 RPM.

Turning the screw in richens the mix, out leans it. You are adjusting air bleed, not fuel flow. It is very limited in it's ability to change the mixture.

Be sure there are no vacuum leaks. Check the throttle shaft for wear. If excessively worn there will be a vacuum leak, the throttle plate will be out of position, the idle stop will not repeat.

Look the governor linkage over for excess wear or slack in any linkage. At idle the carb should be held against the idle stop screw.

MarkB_MI · Sep 21, 2019

Surging idle is usually a sign of a blocked idle passage. My guess is you can turn the idle screw all the way in and see no change.

Carb issue

ascory

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Steve@Advance

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MarkB_MI

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