Generator starts and runs for a few minutes and then shuts down.

Make sure the gas is fresh. Also, take off the carb bowl and look for signs of gumming. If there is gooey stuff in the bowl, then the carb needs to be cleaned.

No wiring diagram available from Briggs. Try re-magnetizing the rotor. No AVR or Capacitor listed in the parts list.

Disconnect the wires to brushes ( pay attention to the order) and apply 12vdc to brushes. Positive goes to brush closest to the bearing. Start the generator and check for output. If output is normal run the unit a few minutes to ensure re-magnetization then shut down normally. After shut down disconnect the 12 vdc source and re-install the previous disconnected wires. Now re start the generator and test for output should be okay provide there is no problems with the alternator. If no output during the above re-magnetization then your rotor windings my burned out.

Is the oil level good, does the low-oil cutoff switch work properly? Try bypassing the aforementioned switch to see if it fixes your woe.

Check oil level, and viscosity is correct 30W etc
Then check oil presure switch and wiring

You have a carburetor problem. Stuck float or clogged filter. Gas cannot get into the carb as fast as it is used. Letting it sit for a few minutes will allow the bowl to fill.

Check your oil level, and make sure the unit is not overheating

There is debri or dirt in gas tank and eventually it gets sucked up and clogs the screen filter on the end of gas line. Drain gas tank and flush out a few times. let dry and put new gas in it. check your gas can, if it is metal, it may have rust in the bottom of it and it goes in the gas tank and clogs screen, make sure you have a clean gas can that you use to fill the generator.

Is there a fault?? All UL listed generators including Kohler are required to lockout on a fault on shut down. This really sounds like a problem with your 2-wire auto start connection between your automatic transfer switch and genset. RDT model automatic transfer switch it is the 2 middle wires on the green connector and terminals 3&4 in the generator. close to run and open to shut down. Any open at any time will cause the unit to shut down. The 12 will shut down instantly upon an open because your 5 minute cool down is built into the transfer switch.

The first thing I would do is to clean and dry air filter. If it is a foam material you can use a warm water and a few drops of dish soap.Rinse thoroughly and let dry. I also would try a small amount of octane booster in my gas. Hope this helps you.

I have an HM100 on a 5500 watt gen with the same problem. This motor calls for a J17 spark plug, but I found using a J19 (hotter) plug solved the problem. I think the J17 doesn't get hot enough for a complete combustion burn so it act like fuel starvation thus resulting in the black sooty and wet plug.