I have recently purchased a used Generac 4000XL portable generator.

1.) I would like to change the oil and filter. The engine is a 7.8 hp; I don't see an obvious manufacturer's name...only OHV. The manual states it should use synthetic oil. I don't know whether the previous owner used synthetic oil or not. If they are incompatible in the same crankcase, since I don't know which one I will have drained out, is it better to refill it with synthetic or conventional oil?

2.) The measured voltage is too high (no-load or with load) about 150 V. There's a protocol in the manual to adjust idle according to rpm. Is there any reason not to adjust it to about 120V while measuring output with a digital voltmeter?

Thank you!

Carl Solomon

Dallas TX