VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 1928 Chevy Four - Engine RPM Fluctuates

Engine has run smooth for years. The engine starts easy and idles fine. Now, after rolling in first gear, if you hold the gas pedal steady the engine rpm fluctuates up and down, kind of a gallop. Same if hold gas steady in 2nd gear. In third gear runs smooth without the rpm fluctuating at all. Engine has plenty of power and no problem accelerating. Does anyone recognize what might be the cause of this? Thanks,Maxie.

Sounds like it may be running rich to me, causing the engine to hunt. Perhaps it is getting extra fuel through the vacuum tank connection to the inlet manifold? This occurs if the internal valves are not sealing (usually a loose seat)and the tank overfills sending fuel down the suction line.
Alternatively is the carburettor float level too high?
Good Luck
Geoff. :)

The internal passages and parts in the carb may contribute. Does the exhaust emit black smoke? Particularly when going from an idle to higher speed. Corrosion in the low speed jet passage is a common problem with the '28 carbs.