The great Walter Musciano once published this advice in a book published in 1956:

Make sure the fuel tank is securely wedged into place or else vibration will cause the fuel to foam in the tank causing erratic engine runs.

Obviously he was able to stop foaming not by fiddling with the engine or the prop but by making darn sure the tank could not possibly move. I suppose it wouldn't hurt to make sure all 4 of the engine bolts are absolutely secure as well.

Robert