I have a B&S on my push mower that runs poorly. I bought it at an auction for $2 because it wouldn't start. The ethanol gas from 3 years ago had gone bad. I cleaned the tank and carb, changed oil, and gave it a few pulls. It fired right up and ran ok. After a little mowing it began to surge and steadily got worse. I pulled the carb again and thoroughly cleaned it. No change. I then purchased a new $13 plastic carburetor, original B&S, for it. New carb and new gasket/diaphragm, no change. The carb is non adjustable. When it runs it surges in RPM and has occasional puff of black smoke. That tells me it's rich. Any ideas???
Engine surges, black smoke
- Thread starter crazy_scooter
- Start date
- Tags black engine smoke surges
Surging is caused by a lean mix.
The black (as pointed out) indicates rich.
The rich mix happens because the governor is reacting to the lowered rpm and opens the throttle valve to compensate.
The rpm then drops again and starts the cycle over...hence the surge.
Check for leaks in the O ring area of carb mount.
The black (as pointed out) indicates rich.
The rich mix happens because the governor is reacting to the lowered rpm and opens the throttle valve to compensate.
The rpm then drops again and starts the cycle over...hence the surge.
Check for leaks in the O ring area of carb mount.
Last edited:
