It does sound like over-fueling, and the old gas could be a contributor.

Before you deep-six the engine, beg, borrow or steal an outboard engine fuel can with the little, built- in squeeze pump bulb thingie. You'll have to cut off the engine end to attach this to your carb, but this will by pass the existing fuel pump and fuel. See if the engine runs OK with this setup.

Carbon from bad fuel can build up quickly. If the above fix works, get rid of the gas. Then pull the plugs and add some Marvel Mystery oil to each cylinder. Turn the engine over by hand slowly and let it soak down onto the rings. Then buy some fresh fuel, button everything up and have another go.

I had a similar problem several years ago, unknowingly purchasing the dregs from the yacht club's tanks - which were pumped out a few days later. The drek quickly fouled the top end. I had 20 gallons of hazardous waste to dispose of....

Well, my space at the club's piers is next to the best fishin' hole on the entire river. I'm always pullin' bottom rigs off my stern lines. Well, some miscreant sidled up to the boat late one night and *stole* all 20 gallons of bad gas. All I can say is "thank you". In a wonderful turn of the karmic wheel, I'm sure he was "rewarded" for his nefarious efforts soon thereafter....

Good luck!