Generac Generator Sitting 5-6 Years With Old Gas — What Would You Do?

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don't know a lot about engines

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Here's your free opportunity to learn! Carburetor engines are very simple.

I had a generac gp6500 I bought in 2019 and it was a great generator. As stated, pull the hose from the tank and drain it and put fresh non ethanol gas. Clean out the tank as best you can and add some star brite enzyme treatment to it and let it run with a load for a several hours. I sold mine to a friend a few days after Ida since I built my own to power my whole house, but I still miss that thing. Purred like a kitten. Friend says it has treated him well.

Drain the old gas, and fill with ethanol free gas. Add Seafoam 1 ounce per gallon of gas. Crank and run under a load. Plug up a fridge or freezer.

Run several gallons through it. The seafoam should clean up any gunk or varnish buildup in the carburetor.

Drained the fuel this morning. About 4 gallons worth. Didn't look all that bad, now I gotta figure out what to do with that. Removed the drain bolt from the carburetor bowl and no fuel drained out out as well as the valve from the tank was in the closed position. I noticed the tip of the drain bolt that goes inside the carb bowl was rusty though. Added fresh fuel and it fired right up. It did surge a little bit while running with no load. I ran it for about 10 minutes. I see this morning after I did all of that that someone posted to run it under load for half an hour so I may go back and do that. I went online and ordered a new fuel filter, spark plug and carburetor just in case. Will change the oil as well. I'm happy it cranked at least so I should be in good shape. Thanks for all of the replies.

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Added fresh fuel and it fired right up. It did surge a little bit

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The pilot circuit is fouled up. Since you already bought a new carb, I would go ahead and install it.

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I see this morning after I did all of that that someone posted to run it under load for half an hour so I may go back and do that.

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Yes, just make sure you plug something in you don't care if it gets screwed up. If it isn't running right, the "dirty" power could cause issues and you won't know until you run it with a load on. I usually plug in an old ice cream maker or something else that's cheap to replace.

I'm not sure who is down voting, but 100% the pilot circuit is fouled up. The generator will open the throttle in response to a poor idle to keep running, the rpm's climb in response .......the rpm's try to drop, but it won't idle well so the surging cycle continues. Under load the throttle is open further, which is why it runs fine under load. These generators have cheap Chinese carbs from the factory, and there is usually little reason to fiddle around with cleaning one that is already varnished and corroded with ethanol. Replace the carb and move on. It's nothing but a few screws. No reason to take it to a shop.

Step one, drain old fuel and oil.

Step two, refill with a decent non synthetic oil (for the moment).

Step three, remove spark plug.

Step four, dump one can of berryman chemtool in tank.

Step four, remove air filter and clean/replace.

Step five, turn engine over enough to get chemtool into the carb.

Step six, wait a few hours.

Step seven, add a few gallons of fuel, e10 preferred to non ethanol.

Step eight, replace spark plug.

Step nine, get it to fire. If you can get it to start, even run on choke, just sit there and feather the choke until it runs on its own.

Plug a blower or larger barrel fan into it and let it run that entire tank of fuel.

I'd say 75% of the time you will now have a functional engine with no carb rebuild.

If it doesn't start... One last hail Mary. Get some Yamaha combustion chamber cleaner, NOT CARB CLEANER. Remove the spark plug, shut the gas off, and spray it into the back of the carb a few times while cranking it over. Wait 30 minutes to an hour and do it again.

Reconnect gas and restart.


For those opposed to ethanol, in this situation it is a solvent.

After you get it running, put whatever gas you like in it. Buy Polaris fuel stabilizer. MEASURE THE AMOUNT, add it, run for 20 minutes or so and shut the fuel off and let it run out.

The Polaris stabilizer is good for two years. The gas in my small inverter is over 3 years old. Started and ran yesterday on the second pull.

I actually use a little two stroke oil in some items, but the Polaris stuff has made me a believer. Doesn't hurt a tiny bottle treats a DRUM