A Puzzle

I made some rpm measurements by using a noncontact tachometer. The engine runs smoothly at speeds between 1500 - 2800 rpm without a load. When belted to the generator any engine speed above about 1600 rpm results in a lot of vibration. I checked belt alignment and tension several times. They seem to be nearly perfect but I don't have a stable setup. Have to go back to the books.

Chinese Diesel Generator - Try #1

Here, the engine is running a 5 kW generator by spinning it at 3600 rpm. With a 4 inch pulley on the engine and a 3.1 inch pulley on the generator, the engine speed is about 2800 rpm, its maximum rated speed. The engine is not too happy at this speed although it makes acceptable line voltage. I wouldn't want to run this setup without standing over it ready to shut it down at any time. Note the distance of the belts from center-to-center.