CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

What's this other adjustment screw on my carburetor?

There’s another adjustment screw on my carburetor, a little bit to the left of the idle adjust screw, a little bit beneath it, pointed more upward, not-seeable when the air cleaner is mounted. It’s the 22 R engine.

The Chilton’s diagrams of the 8, 18, and 20 engines have ‘fast idle adjusting’, ‘mixture adjusting’, ‘throttle position adjusting’ screws, not the 22R’s diagram.

Can you post a photo? I’ve had a lot of experience with 22Rs, but cannot envision your description.

I don’t have a camera, but after putting a stronger light on it I see that the throttle rests against it when its all the way out: it sets minimum throttle. That could have caused my problem, had it been screwed in all the way.

@RandomTroll NO NEED TO START A NEW THREAD IMHOP see

Can’t speak to the 22R carb, but fyi my Ford truck carb has adjustments for

  • idle air/fuel mixture (2)
  • idle rpm selonoid-off (I think this is the same as the screw you describe above, to prevent dieseling problems and prevent the butterfly valve from damaging the throttle seat area)
  • idle rpm selonoid-on ( idle rpm in normal operation, engine warm, either this one or the one above is also called “curb idle rpm”, never can remember which is which)
  • fast idle rpm (idle rpm when engine is cold and choke is enabled)
  • relationship between choke plate angle and fast idle cam.
  • relationship between choke plate angle and choke spring-thermostat temperature

And what, physically, does this do? The throttle rests against mine when there’s no foot on the gas pedal: it sets a minimum.

Yeah I was thinking a fast idle cold adjustment screw. Best you can do with one of those is screw it all the way out. They were a hazard in the winter on ice.
Brakes on but accelerator still spinning the rear wheels.

The fast idle adjustment on my truck’s carb sets the idle rpm when the engine is cold and the choke is still operating. When it is in effect, there’s a little cam that pokes out and holds the throttle butterfly valve open a tad more than it would be for a warm engine.

While I won’t guess what the screw is I did find the specification for the fast idle adjustment and believe it or not it’s 23* with the carburetor inverted and the fast idle cam on the first step according to Motors.

I don’t understand what this means. 23* ?

An angle gauge is commonly used to set the choke adjustment as shown in the picture, on your carburetor a gauge is also used to set the throttle angle for fast idle.

Thanks @Nevada_545. Is there a degree symbol hidden on my keyboard somewhere?

And those feedback Q-jets were great when everything worked according to plans… A nightmare otherwise. Twenty-eight seconds of ticking and 55% duty cycle comes to mind. I still have a drawer dedicated to electronic carburetors and most of the tools are for E4MCs.

° gets you ° in html, which works on this site.