Surging of Car

Karl

Karl

Well-known member
I brought by 1930 Phaeton to work today despitre the fact that it is winter here and we had a frost this am. On driving I noticed that car appears to surge when I'm driving along at less than 15 mph. Accleration seems OK and Ok at higher speeds . Runs fine at idle with no missing. Intially I thought it was just cold but was still doing it after 20 minutes of driving (Model B engine .Model B Carb and 16O Thermostat) Any Ideas Karl
 
Is it possible that you have either just enough of a fuel blockage or maybe a small vacuum leak? Both of which disappear at the extremes of driving?

Mike
 
Surging at low speed as you described is usually caused by the secondary circuit in the carburetor (if it is a Zenith). There is not enough fuel getting to the cap jet. There is a long shopping list of faults that can cause the problem. Try opening the GAV valve slightly more. This will port more fuel to the secondary well. Nominal is about 1\4 to 1\2 turn open. The GAV valve is part of the choke rod. Turn it all the way in clockwise to close it, back it out to open it. Any more than a full turn open and it is full open. You could also have some dirt partially blocking the cap jet and or the comp jet.

Tom Endy
 
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