Throttle Plate Fit

[Pilotdave]

The throttle plate in one of my Zenith carbs doesn't fit tightly to the throat at points around the perimeter of the plate. I can see light at several spots when I hold the throat to the light with the plate closed. I tried loosening the plate screws and adjusting the plate. No change. Tried another plate - same result, so the throat is perhaps out of round (actually, oval) or my supply of plates should perhaps be tossed!

Will the gaps adversely affect how the carb performs?

Thanks much!
Dave

[SeaSlugs]

pssst, where was your idle stop screw set? its supposed to crack open the plate so it idles.

that and they do go in one way due to the taper edge of the throttle plates.

what i do is loosten both screws, loosen idle screw and close the throttle and kinda open close it thus tapping the plate in wherever it wants to seat, then holding it tightly closed tighten the butterfly screws.

[CT Jack]

SeaSlugs perfect answer. I went through this same discovery process and finally realized the idle screw was preventing the plate to completely seal.

[Tom Endy]

When installing a throttle plate in a Zenith it is good practice to back the idle stop screw completely off so that it does not interfere with the closing of the throttle plate. Install the two little screws, but do not tighten them, just pull them down very slightly. Open and close the throttle plate sharply a number of times to seat the throttle plate properly in the throat of the Zenith. While holding the throttle plate closed, tighten the two screws. Then screw in the throttle stop until the small idle hole in the throat appears above the throttle plate. If you split the hole half way the car will start up with a high idle that can be re-adjusted after the car is running.

It has been my experience that many of the throttle plates floating around the Model A hobby are either worn originals or improperly made repos. A poorly fitting throttle plate will cause the car to stall when it comes to a stop because of an improper transition from the run mode to the idle mode.

Snyder's catalog indicates that the throttle plates they sell have been made to the original Ford drawing with the edges ground to the correct angles. That being the case,I purchased a number of them and installed them in Zenith's I had overhauled that would continually stall at a stop. The Snyder throttle plates corrected the problem in several Zeniths.

Tom Endy

[Pilotdave]

Thanks for the great replies, guys. I THOUGHT I had backed off the idle stop screw when I was trying to adjust the throttle plate, but I will check. If I don't see a good fit, I'll try replacing the plate with a good new one. BTW, the car wants to stall at every stop.....

Dave

[Synchro909]

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Originally Posted by Pilotdave

Thanks for the great replies, guys. I THOUGHT I had backed off the idle stop screw when I was trying to adjust the throttle plate, but I will check. If I don't see a good fit, I'll try replacing the plate with a good new one. BTW, the car wants to stall at every stop.....

Dave

Dave, Does the car idle when you are already stationary? If so, the problem isn't the carburetor butterfly valve. For an engine that stalls when you come to a stop, look at the float level. It might be too high. If so, lower it by putting a washer (or two) under the seat.

[Pilotdave]

Pulled the carb off today and reset the throttle plate. Idle speed screw was completely disengaged. Reinstalled carb, road tested and reset idle, then road tested again. Seems much better - no stalling on stops.

Thanks for all the input!

Dave

[Dino's A]

When I reset the throttle plate, I do it the way Tom Endy desribed and I use some blue threadlocker on the throttle plate screws. You don't want those getting loose.

[SeaSlugs]

Originally Posted by Pilotdave

Pulled the carb off today and reset the throttle plate. Idle speed screw was completely disengaged. Reinstalled carb, road tested and reset idle, then road tested again. Seems much better - no stalling on stops.

Thanks for all the input!

Dave

Glad to hear!