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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.

Does the engine have a low oil shutdown sensor.

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?

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

bertsmobile1 said:

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

Click to expand...

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.

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

bertsmobile1 said:

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

Click to expand...

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.

RobSC said:

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?

Click to expand...

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

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.

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.

Problem solved! I removed the wires from the oil pressure switch and the engine now starts/runs perfectly. The original 4PSI switch (#77667) is NLA, and it seems as the substitute part is an 8PSI version (#99236). I'll be ordering this part (along with a new spark plug just as good insurance) and getting this older generator back in operation! Thanks everyone for your help on this.

air filter off, short squirt of carb cleaner in the throat of the carb, close choke, does it try to start. yes / no?

RobSC said:

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

Click to expand...

Check air filter as well. Some original Generac branded filter were made in Malaysia and were treated with a fire retardant....so much so that it restricted intake. Just remove and see if it makes a difference.

Spark and fuel. That's all it takes. You know you have spark but fuel is questionable. Have you blown the carb passages with air? Soaking does nothing to physical particles.....

you mentioned you disconnected your oil level sensor. Generally, the "Run / Off" switch is also connected to the one coil kill wire that goes to the coil. you might see a two into one pigtail connector. disconnect both to rule out the oil and run stop switch.

Did I miss where you checked the air filter? Mice like to nest in resting equipment.

think it was fixed a couple days ago...

Had Gen. the filter screen was eaten away clogging the shut off valve, also had carb. problems. Was not run for 12 years.

Wow! All this help does not start at the beginning. First, does it have a fuel shut off electrical device on the bottom of the carb? Is it quitting because of an engine problem or is spark shut down and it quits suddenly? When it quits does it sputter and stumble or simply quit firing? Does it have a controller, a co monitor, is it dual fuel, does it have a code indicated on the led panel, is it electric start? Basic diagnostics before just taking things apart and hoping for the best. Get a cheep inline spark tester and start with that.

edit: I see you say faulty oil switch - solved. These sometimes stick to the bottom of the oil pan. Disconnection, run for 1/2 hour, try retesting with it connected and often the problem is gone. I have two generator cardcases here because the oil sensor is disconnected and it ran till low on oil and failed.

VRR.DYNDNS>BIZ said:

Wow! All this help does not start at the beginning. First, does it have a fuel shut off electrical device on the bottom of the carb? Is it quitting because of an engine problem or is spark shut down and it quits suddenly? When it quits does it sputter and stumble or simply quit firing? Does it have a controller, a co monitor, is it dual fuel, does it have a code indicated on the led panel, is it electric start? Basic diagnostics before just taking things apart and hoping for the best. Get a cheep inline spark tester and start with that.

edit: I see you say faulty oil switch - solved. These sometimes stick to the bottom of the oil pan. Disconnection, run for 1/2 hour, try retesting with it connected and often the problem is gone. I have two generator cardcases here because the oil sensor is disconnected and it ran till low on oil and failed.

Click to expand...

It's a really simple B&S motor on a generator that I think is a 1990's model. So, besides the low oil sensor there are no other safety or control devices/circuits that you might find on a more modern generator (simpler is better!). It does have electric start and it spins the motor over no problem regardless of the position of the run/stop rocker switch. I checked/did all the simple stuff prior to tearing anything apart - checked no obstruction to the air filter, oil level was correct, no loose/chewed wires anywhere, squirted some carb cleaner in the intake, etc. I was initially trying to get this machine going during a power outage so I desperately wanted to find the quick/simple solution first! When it was shutting down on it's own it would seem to just quit firing - as if you'd flipped the rocker switch to "stop". Only difference is that the engine would run for about 5-10 seconds before shutting down, whereas flipping the rocker is an immediate loss of spark. I don't have a spark tester, so I couldn't test to see if/when the spark stopped in conjunction with the motor shutting down. Since I didn't see anything physically wrong with the electrical side of things I was going down the path of a fuel supply/carb problem. My suspicion of a fuel problem was heightened when the generators' owner told me he had left gas in it for 3+ years yet seasonally started it to check operation. It had run on this old gas for a short time before fresh gas topped off the tank. Then the generator quit running and here we are.

The low oil sensor isn't a float type, so no moving parts to get stuck anywhere. It is a pressure sensor that is picking up the oil flow right at the spin-on oil filter. Removing the wires from the sensor allows the engine to run normally. During diagnosis of anything I always try to only change one thing at a time to see what the effect will be. In this case removing the oil sensor wires and changing nothing else made a positive change. If I physically follow the wires it seems that the oil sensor wires and kill wire to the magneto are in parallel loops - both of which are connected to the run/stop rocker switch. Chuckpen alluded to this wiring scheme when he mentioned that the rocker switch would have a 2 into 1 pigtail on one pin of the switch. Without a wiring schematic to reference I am assuming that in operation the grounding of either the oil pressure switch circuit or magneto wire will kill the motor with the rocker switch being the manual way to shut it down. When following the oil pressure switch wiring I see it goes into the control panel for the generator and connects to a PCB inside. I assume there is a delay circuit on the PCB that stops the motor only after a set time of no/low oil pressure. This makes sense to me since if it didn't have this delay circuit the motor would never be able to start as there might not be enough oil pressure when initially starting the motor to allow the magneto to make a spark.

So I can see 3 places where the oil switch circuit could be faulty - the rocker switch, the oil pressure switch, or in the control PCB. Since I only removed the wires from the oil switch and that allowed the engine to run then this means something to do with the oil switch itself is causing the circuit to be grounded and all other parts of the circuit are OK. Conversely if it were a fault in the PCB then there would be no change and the motor would still shut down after 5-10 seconds. I haven't done this, but if I put an ohm meter on the suspected faulty oil switch I would expect to see it is a closed circuit regardless if the motor is running or not (a good oil pressure/non-faulty switch would be an open circuit when running). But this wouldn't tell me if the switch is actually bad though as the switch could be correctly sensing that there is in fact not enough oil pressure so it would remain closed when running. If when I install the new oil switch and the switch remains closed while running then there is likely a fault with the oiling system and I can diagnose further. If the switch was big money I would have diagnosed it further but it was only $10, so I took the chance it is the switch that failed and not the oiling system. A second reason I suspect the switch is bad is because when I removed the wires from the terminal the whole terminal post was loose and rotated within the switch - something that I'm pretty sure it is not supposed to do. Even if the oil switch is still operating properly I'd want to change it anyway to fix that issue, so it wasn't money down the drain for a new switch as far as I'm concerned.