a friend of mine had a similar problem,it tried to drive me crazy,it ended up being the check valve on the tank,had some metal chips stuck in it,i just omited it from the system,no problem since then.good luck.

Chuck,

Hope you get it figured out soon man. Hate that it messed up the poker run for you.

I've got a 312 fastech with twin 454mag mpi's and they vapor locked on me several times this weekend. I too am looking for the fix. When cool they run great. I let mine cool at the dock for an hr then idled out past the no wake zone got on plain and the poof vapor locked, one re-satrted and the other had to cool I'm running 155 temp one one motor and 165 on the one that I have to let cool...I't a Bull-S__T design if you have the VST's, On our formulas the heat rises and has no place to go.. I may add another set of fans to evacuate the heat at the top of the motor where the problem is...Not to mention the pump change in the VST.. good luck...

Here is a real good thread on the 502 vapor lock issue, lot's of good ideas.

http://www.offshoreonly.com/forums/g...apor-lock.html