On Tue, 29 May 2012 01:51:22 -0700 (PDT), Hank
wrote:

Since we can only guess, I would do the following.............

Check to make sure the vent is working onthe gas cap.

Loosen the cap 1/8 turn or use a paper clip the clear the vent hole in
the cap. A vacuum builds in the gas tank, so the engine starves for
gas. But sitting for a while the vacuum releases slowly.

Change spark plug.

Ceramic on the plug can crack (done it in my repairs) causing a short
to ground (sudden shut off).

Start simple :-\