zenith carburetor experts

mkuhns · Jun 20, 2021

I have a zenith 63awll updraft carburetor on a tractor that came off a 248 chevy. It's currently on a 283 waukesha. It works good and lugs fine, but can't get enough fuel out of it under load. I drilled out the main jet some, but now that affected my idle circuit. It over fueling at idle no matter what I do except to turn in the load screw and then you don't have enough fuel under load. What do I need to do to get some more fuel out of load circuit? Any help would be appreciated.

Steve@Advance · Jun 20, 2021

Is the float level set to specs and the needle valve closing, no evidence of flooding?

Changing the main jet should not effect the idle mixture.

If that carb is like most updrafts, turning the idle screw in richens the mix. The screw adjusts air bleed, not fuel. The idle mix will only adjust when the engine is at dead slow idle, anything above 500 RPM or so will be picking up the midrange circuit.

Check the idle air bleed to be sure it is not clogged or the wrong top gasket is blocking the hole.

Be sure the throttle plate is correctly installed and not bent. With the idle stop backed off, the throttle plate should close completely air tight, fit perfectly in the bore.

Didn't find your exact model, but this should be pretty close.
Zenith Carb

mkuhns · Jun 21, 2021

Yep, idle circuit is the one u sent a link to. I actually removed that air bleed office and nothing changed, still rich at idle. Throttle plate goes tight and the gasket isn't interfering with any of the passages. I ran a piece of wire through all the holes in the carb. It doesn't flood itself like the float is letting in too much fuel either. I'm thinking its getting fuel from the main nozzle now instead of the idle. Idle circuit worked fine before opening the main jet. That's what's puzzling me.

zenith carburetor experts

mkuhns

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Steve@Advance

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mkuhns

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