Need help, at wits end. Here's the situation. 1983 Yamaha QT50 or yamahopper, ugly yellow color. Been sitting at Dad's house since 1985. I have a 1980 QT50 that I use for parts. Anyway, cleaned out the gas tank, new fuel line with filter, couldn't get all the crud out of the tank. Took the carb out and luckily it had oil in it so all the parts were still good and not trashed. Tore it all apart and cleaned it. The bowl and all the jets, and needle valves were in good shape. Popped the head off and cleaned top of piston, reassemble. Took the cover off and checked the capacitors and wirings, all in good shape. Took muffler off and cleaned it. Took the autolube pump out and cleaned it and bleed the air off when I put it all back together. Checked the wires coming off the stator and they all checked out with an ohm meter according to specs. I have the maintenance manual for it. Relubed all the cables and all working as they should.
Got it running the other day, ran fine. Don't have a battery for it and I'm using the original spark plug, get good spark from it and it's gapped right. Drained the transmission oil and put new 10W-30 in it, as per the book.
Here's the problem. It will crank up fine, idle and rev up, no problem, but after a few minutes, it will simply die. I checked the gas drain on the bottom of the carb, it has gas and I can see it in the filter, so I know its not starving for fuel. I know the oil pump works because of the exhaust color. I put a new air filter on it. I don't have a battery on it, but all the lights work fine when she's running. Before it dies, and your giving it gas, you can hear the carb moan, so it should still be getting gas in it.
What the hell is going on? Ideas, suggestions? Could it be the spark plug?