B&S on Generac generator won't stay running

[RobSC]

The issue I am having with the machine is that it was used for a short time (less than 15 minutes) during a recent power outage. It was running fine and producing power during this time, but then the engine just stopped running. I can get it started again pretty readily, but it will only run for several seconds then stop. I found out from the owner of the generator that he had left gas in the unit from when it was last used 3+ years ago, only occasionally starting it up for a few minutes to check that it still ran. I found the fuel filter was clogged (or at least I couldn't see any fuel going through it), so I replaced it along with rebuilding the carburetor using a genuine Generac kit for the Nikki A4600 carb that is on the motor. I also completely drained the gas and refilled with fresh fuel. The problem still persists. The generator side of the unit seems to be working fine as I do get voltage during the short time the engine runs so I don't think something on that end is causing the problem. Startup looks like this: from cold I choke it, hit the starter and it fires right up, I move to half choke and at about this point the engine conks out, sometimes I can get it completely off choke before it dies, but I can't get more than 10 or so seconds of run time. I can then immediately give it at least 1/2 choke and hit the starter and it fires right up again after a little cranking. There are no fuel leaks anywhere and the carb kit I got included new intake gasket, needle valve, float, etc. but no welch plugs so I am only able to flush the carb with cleaner to know that all passages flow free.

I'm at a bit of a loss here as this problem seemed to spring up with no indication of running rough or stalling etc. beforehand. I suspected the problem was caused by that really old fuel, but now I'm thinking the fault is elsewhere as I've cleaned and refurnished all of the fuel system at this point.

The unit is a Generac Beacon model # 01277-1, series # 7200 BPS, S/N 6187553

EDIT: Fixed the problem. Turns out it was a faulty oil pressure switch.

 

[ILENGINE]

Does the engine have a low oil shutdown sensor.

 

[RobSC]

It does have a low oil shutdown sensor. The oil level in the motor is good, and the LED for the sensor isn't illuminated. I supposed the LED could be faulty so I'm not seeing it falsely report low oil. Is there a test I can do to see if the oil sensor is putting out the correct signal, or bypass it somehow?

 

[bertsmobile1]

Start from the begining
1) is the fuel from the tank getting to the carb ?
most generators have an in tank fuel filter / strainer which clog up with rust .
Old fuel can attack fuel lines causing them to swell inside and block off supply

 

[RobSC]

Start from the begining
1) is the fuel from the tank getting to the carb ?
most generators have an in tank fuel filter / strainer which clog up with rust .
Old fuel can attack fuel lines causing them to swell inside and block off supply

Thanks for the suggestions. Forgot to say earlier that I also replaced the fuel line between the carb and fuel filter not because it was swelled but because it was so darn short I had a hard time trying to re-attach the new fuel filter to it. I replaced it with fresh hose and confirmed I get flow from the tank, through the shutoff valve & fuel filter. The fuel tank is all plastic, so there should be no issues with rust and I don't believe there is any other filter inside the tank. Plus I've checked the flow so even if there was one in there it is flowing fine. I've also cracked the fuel cap in case the vent was plugged, but that made no difference either.

 

[bertsmobile1]

In that case the idle jet is clogged or the float is too low .

 

[RobSC]

In that case the idle jet is clogged or the float is too low .

Not sure which part on this carb would be the idle, but both the large brass one inside of the float bowl and one that is located under a screw that is on the outside of the carb are clean and free flowing. When I reassembled the carb with the new needle and float I made note that the float was parallel to the carb when held upside down. As far as I can see there is no adjustment on the height anyway as the needle clips into the float and the seat appears to be brass and pressed into the carb and wasn't removed as the rebuild kit didn't include a new one.

 

[ILENGINE]

It does have a low oil shutdown sensor. The oil level in the motor is good, and the LED for the sensor isn't illuminated. I supposed the LED could be faulty so I'm not seeing it falsely report low oil. Is there a test I can do to see if the oil sensor is putting out the correct signal, or bypass it somehow?

You should be able to disconnect the oil level sensor on the side of the engine block.

 

[RobSC]

Just an update: I took advice and went through the fuel system again by taking the hose off the carb and confirming good flow from the tank. I also pulled the spark plug to check if it was wet or dry after trying to run the engine again. It was dry, but very black and sooty. I don't have a replacement handy so I cleaned it with a brass wire brush and reinstalled it. No difference to the problem. I will try disconnecting the oil sensor next and see if that does anything.

 

[bertsmobile1]

That plug is now trash
The brass will have created tracking paths down the insulator nose .
Get a fresh plug
Remove the blower housing and the kill wire from the magneto
When you get a new plug try that to determine if your problem is with the fuel system or he ignition system.