I've been able to get the thing to backfire. Last time, it happened twice in about a 10 second span. At the second one, I let go of the starter button and heard the thing suck air and fuel into the chamber. Sounded like a 90 year old smoker gasping for air.
But I can't get the thing to crank for more than 15 seconds before the battery just won't turn it over. Even if the thing is connected to the battery tender, it only last 15 seconds. The battery is being a little weird. If I put the volt meter on it, I get 12.5 volts right away. But if I leave the probes on it, the volts just keep climbing about 18 volts.

Anyone have an idea? Is the backfiring a good or bad thing?