Brian Stephenson wrote in message ...
My dad's GM305 (5L) Volvo was doing same thing. Tuned up, rebuilt carb,
new coil, no better. Removed valve covers, no broken rockers or springs
but one lobe on cam is just about gone. Very hard to change cam without
pulling motor. Changed prop to bring rpm down. Has been exceptable for
three years now. He doesn't leave the dock a whole lot though.


Chevy small blocks had the popping problem, caused by worn cam
lobes. A worn lobe fails to open one exhaust valve sufficiently, and
the exhaust gas pressures that remain in the cylinder after the
exhaust stroke will pop back into the intake on acceleration.
Cylinder pressures tend to be highest at acceleration.
Another cause could be lean mixture, but that's usually only a
problem when the engine is cold.

Dan