I have a Homelite generator powered by a Briggs 8 HP engine. Checking the output I find that the 120 is putting out 140volts and the 220 is putting out 280volts. This generator is more than 15 years old with maybe 100 hours of operation. What if anything is wrong?
Homelite model EHRL4400HD SERIAL #HP0870443 33 AMP

It may not be a anything wrong. Many times the over voltage is caused by lack of load. Are your tests being run while under load? That will tell you the difference. In most generators voltage can vary. So be sure to check it both ways.

I would think that either regulator failure or governor failure would be to blame. Might be difficult to sort out without a frequency counter.

Check the throttle/governer linkage and make sure it's free.