Help needed with Generac Generator

I am trying to get my dads Generac 4000XL working for him but would appreciate any advice as to where to start as I am new to these things.
The two obvious problems it has are:
1. It starts fine but shuts down after about 15 seconds.
2. At idle it has power to supply a light, my dremel and even seems to want to run my skill saw but rather than throttle up under load it simply bogs down when a heavier load like the skill saw is added.
I have found that I can prevent it from shutting down if I disconnect the connector leading to what appears to be an oil pressure sender. Before I did this I checked the oil level to make sure there was plenty. Oil actually came out the fill hole so I guess it must have been over filled.
I think my dad took it apart to try and fix it but is not sure it was assembled properly. Also my dad thinks that he burned out his radial saw trying to operate off the malfunctioning generator.
If anyone can suggest possible causes for my problems I would be greatly appreciated.
Thanks
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For oil to pour out a motor indicates the float stuck pouring gas into the crankcase, change the oil and turn the gas valve off when not in use. Was the oil off color or smells of gas, you can ruin a motor with diluted oil.
The unit does not realy idle, run rpm is 3600 , idle controle is apx 2200 rpm, try turning the idle control switch off to leave it at 3600 rpm. Does the throttle linkage move freely, are you sure the choke is off, on my 7500 generac if choke is towards the choke label it is actualy on, an arrow points to off, it took me years to figure their backwards label out. Is the unit clean, dirt or something might be affecting the govenor from keeping 3600 rpm,
3600rpm0v`hz. You can get a 20$ tachometer-hr meter to be sure you run 3600 or use a volt meter to adjust under load you normaly need to keep 120v.
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Apparently that is not an uncommon problem with the Generac products... I have the same thing with my brand new Generac pressure washer... Spoke with the manufacturer about it and they said that I need to replace the sensor... Instead, I just disconnected the wire...
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