I think something like this was brought up before, but not certain, maybe someone remembers.
Rpm range 1200-1500 engine. If this is non inverter, which is likely, that is a 20% variation in frequency. OK for resistive stuff, but not a lot of other things. Motors run fast or slow.
Voltage regulator "optional"?
Unknown how to handle 120v under the hood in heat and vibration, might be safety hazard if shorts to chassis or other electronics.
If it was a good, clean power, run any rpm inverter generator, then I think it might have some good promise.