| : : Hi All, : : My '30 Coupe idles best (when warm) with the gas adjusting valve at 1/4 turn open. To drive at speeds of 0-25 mph or so, I need to open the valve up to about 1/2 turn. For faster speeds (I haven't had the nerve to go above 40 mph yet) it runs best at about 1 turn open. Further open than 1 turn doesn't seem to make any difference. When I am about to start from a red light (where it idles at 1/4 turn open), I find it best to open the gas adjusting valve to 1/2 turn BEFORE stepping on the throttle (it complains, backfires, etc if I don't). : : Are these settings and procedures within the "normal" range for the gas adjusting valve? : : Thanks,
: : Paul : Paul,
: Just to let you know you aren't alone, my Zenith runs almost the same as yours. I'm sure there is some deficiency in the high speed circuit that causes this. Mine idles great at about 1/4 turn open without any rolling or loping. But you try to get on down the road with it at that adjustment it spits and sputters. I have to go to about 2 turns open to run at 40 and can easily go up to 50/55 if need be at that setting.
: I haven't tried to fix this as I put up with the rolling and rough idle when driving rather than adjust the gas mixture at every stop. Been driving it this way for several thousand miles and it doesn't seem to hurt anything except it is bothersome at either touring speed or idle.
: I'd be glad to know what you find out about your experience.
: John Hello Paul and John,
The theory of the no moving parts Zenith carb (no accelerator pump) is that the secondary well will fill with fuel while you are running along at steady throttle or idling at a traffic signal. The fuel in the secondary well is then available at the Cap jet which is the one right next to the main jet. When you start out or stomp the go pedal, the fuel in the secondary well enriches the mixture and all is fine. As the secondary empties fuel can move from the bowl thru the compensator jet to the cap jet. This is less than when the secondary is full.
You both seem to have fuel starvation when accelerating which should mean that the secondary is not supplying fuel and since you both seem to run lean after acceleration but with a lot of throttle I'd say you may have a clogged compensator jet or two. The gas adjust valve uses the cap jet to enrich the mixture so I think the problem is the compensation jet but you should clean and carefully inspect the entire carb.
Hope this is helpful Ray
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