Onan 4000 won't start while warm

[HUGHP]

Lately our 8 year old Onan 4000 genset starts and runs every time if cold but when I try to restart the unit after gassing up at a gas station it sputters and won't start. It cranks up again just fine after 45 minutes or so. Can anyone offer an explanation or cure? BTW,I run the genset at least 1 hour each month.

[bigskymt]

You may be experiencing vapor lock and a weak fuel pump is unable to overcome it.
The voltage to the pump drops when cranking the starter so the pump is trying to run on reduced voltage.
Check your fuel line where it connects to the pump, a loose clamp will cause you to suck air.
If you engage battery boost when trying to start the gen. it may provide enough extra voltage to the pump.
If you feel comfortable checking pump output pressure and volume both hot and cold that will narrow things down.
Likewise input flow to the pump.

[HUGHP]

Thanks,I'll check the fuel line. Not sure if my coach has a battery boost onboard.