a friend of mine has an old TT 40 GP on a homemade airboat. it hasnt been run in a loooong time, maybe 10 years or so. Last weekend we started it up, it ran for about 30 seconds fine then just quit. it wouldn't start after that no matter what we tried. changed the plug, tried different glow igniters, primed it sufficiently and everything. the fuel wasn't bad because it's the fuel i've been using in my planes, and my .40la (which i hear is just the o.s. version of the 40gp - cheap bushed motor) ran fine 5 minutes later on that fuel. any ideas what could cause an engine to start up on the first flip, run for a few seconds, then just stop working altogether?

thanks