Maybe it is just me, but I'm thinking you need major gear reduction between that engine and the DaVinci drum!
I'm talking slow enough so that you can distinguish each individual drum beat. Smallest pulley on the engine flywheel shaft to the biggest pulley on the generator, then the smallest pulley on the generator to the biggest pulley on a line shaft, then smallest pulley on that line shaft to the biggest pulley you can fit on the drum.
Then run the engine just as slow as it will go!