Generator hard to start and backfiring

My son in law drained the carborator 3 times to get the old gas out. Also put in an additive to the gas. He figured our unit had sat too long and the gas was getting old. It is running fine now. Just need to figure out how to idle it down.

Check the fuel pump, if it is a briggs engine it most likley has one

check the fuel mixture settings i believe main screw is 1 3/4 turns from closed and the idle screw is set at 1 1/4 turns from closed. These settings are for non OHV models. also check that if you have a fuel filter installed that it is not plugged up.

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.

Changed plug since last year?Choke adjustment? try premium gas?

If you have fire coming out of the carb, then your intake valve is stuck open. Take the head off, and as you turn the engine, tap on the valve with a plastic screwdriver handle to make it go in, then turn it more to push it back out. If you need to put a light coating of oil on it, so be it. Keep doing this until it's freed up, then put it back together.

Sounds like the timing may be off or maybethe exhaust valve maybe hanging open.

check to see if it has a smeared or worn key way it is what times the fly wheel to the engine if not it is possible that it coul have problem with a valve or engine timming

To maybe convert your Flamethrower back to a generator, Make sure the fuel line is a good quality thick rubber material (like OEM )since it passes through the engine,HEAT is a issue, if it has been modified to steel, or it's thin rubber, it will overheat the fuel on its way to the carb and cause backfires after the engine warms up , ( vaporizing gas and pressure bypassing the jets flooding the engine) I use 1/4 inch Goodyear sold at Autozone , one of very few name brand quality parts you can get there. The other possible cause is carbon deposits built up on the leading edge of the valve not allowing the valve to close all the way, just clean the valve, it is caused by too lean or rich carb setting or clogged jets, if it is a newer style carb with a pink main jet then debris in this area will always cause backfire, check and make sure the old tiny O-ring on this jet is not still in the bottom of the shaft, people forget to pull them out all the time or give up trying to pull them out, I use a paper clip and bend the end 1/8 of a inch @ 90 degrees to fish hook it out of there, CLEAN THE SHAFT with carb cleaner and a Q-tip.... A Tecumseh engine will always backfire if the carb or airflow is not perfect and sealed tight !!!!!! it looks simple to rebuild the carb but you must take your time and look close, clean it very well, make sure the jet is SEATED properly and all tiny holes are clean, use guitar string not torch head cleaners as they will enlarge the holes and make your carb run rich.

you could try a briggs and strtton dealer as they took over generac but think with it being a tecunseh engine you will have a big problem as that side of the company went under a few years back,sorry cant be of more assistance