Re: Engine dying on hard stops

Posted by Glen Weilbaker on April 09, 1998 at 13:07:13

In Reply to: Engine dying on hard stops
posted by Dick Sparks on April 08, 1998 at 07:14:23

Mr. Sparks,
The zenith by design has the problem you describe. What happens is the fuel in the bowl moves foward away from the jets during braking thus starving the jets. The stalling can be minumized by adjustment of the idle circuit.
The best desciption of the procedure is in Paul Moller's Carb. Handbook. I'll try to give you brief a one if you don't have this book.
First, a little understanding of the carb. Not all carb idle screws do the same thing, meaning your '55 Belair may control the gas, Chuck's'66 Norton controls the gas/ air and Carl's '58 Cushman the air. The zenith does the air and because of this there is interactivity with other idle adjustments, so a procedure of events must be done to get it dialed in.
1. Good carb, the throttle shaft bearing should not be worn out. Air is drawn in and proper adjustment will not be possible.
2. Clean carb, All those little passages have to be clean.
3. The engine must be in good tune.
4. Bench adjust carb, mainly the float and 1 turn out with the idle air screw.
It sounds like you have these already,
4. Warm the engine, set the spark about mid point, set the mixture knob about a quarter turn out. Then set the idle speed screw, the one on the throttle, to about the idle RPM.
5 The fun part adjust the air screw , in should be rich, out should be lean, the RPM will change and re adjustment of the speed screw maybe necessary. Every time the speed screw is moved, the air must the adjusted to compensate. This part will take some twidling to get the right speed but always end by adjusting the air screw.
Another thing to realize is the zenith is a unit of compromise, get the idle perfect it's gonna die on stops, so twik the air screw a tad rich.

I had the same problem, it took a few stops to set the air screw.
Good luck and let the board know what you found,
GW

: My 31 A runs and idles great under normal driving conditions.
: However upon hard breaking the engine will die. I can increase the idle with the throttle while stopping and keep it running. I have listened to the engine while making stops
: and determined some loss of rpm even on normal stops. I was
: advised to raise the float level in the carburetor (Zenith1)
: and did so with no noticiable improvment. This does not occur
: in reverse, only forward. I cleaned the filters and checked the fuel flow which all seemed normal. Gaskets were replaced
: and no air leaks can be detected. The carburetor was cleaned
: and no problems were visible. Any ideas?

Follow Ups:
correction GW April 13, 1998 at 12:48:02(0)

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