Generator not starting

[Stude55Dog]

Just got new to me 07 Raptor with gas 5500 Onan generator. Issue is you can run it five minutes or 5 hours, but the minute you turn it off while hot, it will not recrank. Changed fuel pump and filters, fresh gas. Tried re priming, no luck. Any suggestions what to try next? Thanks

[bounder39zman]

these generators tend to be hard to start when hot. Problem is
they have a mechanical governor system, and governor spring holds throttle at wide open position when not running. when engine is cold, choke mechanism richens up fuel mixture sufficiently to aid in starting.
But when choke is off (as in hot engine), the wide open throttle causes there to be very low vacuum in carb, and fuel is not being drawn in
adequately to start at low cranking speeds. If some of carb jets/ports are partially varnished from long periods of not running, this makes problem worse. a new carb or really good cleaning may help, but only other fix I can offer is to manually close choke by hand if you need to restart a hot engine. hope this may help

[Hank_MI]

RSD559 wrote:
If this was an old car, I'd suggest maybe vaporlock. Where the fuel in the carb vaporizes due to heat. Until the carb cools off, no go.

Actually that's not what happens with vapor lock. Vapor lock occurs when the fuel in the supply before the fuel pump vaporizes due to heat. With vapor in the line the fuel pump can't create enough negative pressure to pull gas from the tank.

You can consider the gen as an old car since the fuel pump is located at the gen and uses suction to draw fuel from the top of tank, pretty much like an old carbureted car. Pretty sure all cars now have the pump submerged in the fuel tank which solves the vapor lock problem since it pushes gas to the engine rather than trying to use negative pressure to suck it from the tank.

EDIT: I said the fuel vaporizes in the fuel line. It vaporizes in the fuel line before the pump or in the pump itself.

[RSD559]

If this was an old car, I'd suggest maybe vaporlock. Where the fuel in the carb vaporizes due to heat. Until the carb cools off, no go.

[Sam_Spade]

Stude55Dog wrote:
I have run this generator for hours and it does not shut down. It is only trying to restart immediately after shutting it down or shortly thereafter. Thanks

Sounds to me like you have a problem with the automatic choke sticking partly closed. Is your exhaust pipe REALLY black ??
The Cummins/Onan shop in Ocala has been REALLY good to me.

[Stude55Dog]

I have run this generator for hours and it does not shut down. It is only trying to restart immediately after shutting it down or shortly thereafter. Thanks

[Stude55Dog]

If I let it set for an hour or more it can be started. But immediately after running and then trying to restart it will not run. Must be some issue with being hot? I do not have a parts manual, but where is the spark plugs on this model and are they easily accessed. Thanks

[MrWizard]

check for spark

most likely suspect is the control board

it could be failing and once warmed up decides the engine is too hot to run aka shut down is enable until board cools down

[Stude55Dog]

Will not restart. The starter turns engine over but it will not restart. Oil is checked and good. Thanks

[RSD559]

Stude55Dog wrote:
Just got new to me 07 Raptor with gas 5500 Onan generator. Issue is you can run it five minutes or 5 hours, but the minute you turn it off while hot, it will not recrank. Changed fuel pump and filters, fresh gas. Tried re priming, no luck. Any suggestions what to try next? Thanks

Will not crank, or will not start?