[Bleach]

I know many may cringe at my method of priming a carb on a car that sits. I just pour a few ounces of 40:1 2-stroke mix gas right down the carb. Sometimes it takes an extra few ounces of gas to get it to run enough to fill the carb. Once it's filled, the air cleaner goes back on and I'm on my way.
I've never had a back fire or any accident in about 40 years of doing this. Do it at your own risk though and keep a fire extinguisher handy just in case.