Thanks for your reply trader4.

I understand all that's been said about backfiring causes but it's
hard for me to believe that turning off the gas did something that
caused the timing to be off which thus caused the backfiring.

The spark plug condition is good and the spark is also good. The gas
did have fuel stabilizer in it.

The backfiring occured when the fuel level had dropped very low, not
quite empty. Perhaps there was floating junk in the fuel and it got
into the carb only when the fuel dropped to a low enough level.

I think your tip to rebuild the carb will be the next step.



On Sat, 20 Mar 2010 08:06:29 -0700 (PDT), wrote:

Did it have fuel stabilizer in it while it was sitting for a year?
Even if it did, my first suspicion would be that the carb is fouled.
But usually that doesn't lead to backfiring, just not starting. On
the other hand, the backfiring did start when you turned off the
gas. If it was timing related, a valve, etc, curious that it started
just when fuel was shut off. I suppose the float could be stuck open
flooding it badly.

After checking the spark plug condition and for spark, I'd pull the
carb and rebuild it. If you get a service manual it should be fairly
easy. By taking it apart, you can completely clean it and remove any
gunk. The rebuild kits are cheap, look on Ebay. I got one for a
Tecumseh engine for ~$12.