Re: Weird Surging

Posted by TxGoat On 2024/2/23 10:59:36

Carburetor float level can be critical.

Does the surge problem occur at lower altitude the same as at higher altitude? Does engine temperature or ambient temperature seem to affect it?

Carburetors depend on air pressure differential to function, and so do conventional fuel pumps. At higher altitudes, less differential is available to move gasoline through the carburetor circuits in any particular operating mode. Perhaps a float level setting at the high end of spec, or even a bit higher, might help if you have a lean surge. A rich surge would require smaller main jets or a revised power valve setting.
Gasoline will vaporize more easily at high altitude, which would favor vapor lock, and conventional fuel pumps will lose efficiency at higher altitude. The combination of altitude, modern gasoline blends, and normal operating heat might induce mild vapor lock under load. An auxiliary pump located near the gas tank would prevent any fuel delivery problems related to reduced stock fuel pump efficiency.

Carburetor "icing" could be an issue, though that usually occurs where humidity is readily available.