Instead of 120VAC; meter reading 8.5- 10 vac going to the 45 amp circuit breakers; and the same going to the fan circuit breaker. However, fan is not running at all. Generator starts and runs OK.
There has been a thread on this subject before. Try doing a search.
On the voltage regulator, locate the F+ and F- wires, mark to keep clear which is which, using a 9 volt transistor battery, while running the engine connect the battery and read the generator output voltage, no load, breakers off including the fan. Voltage should read about 100 volts. If so, you need a regulator, if no or very low reading, you need to remove generator to determine if it is the rotor or stator issue.
With your reading of 8-10 volts would normally indicate the regulator issue.
Very simple