I have a '96 Formula 336 with a pair of 502/ 415 HP Mercs.
If I run the engine for a couple of hours, and then shut them down for about an hour, they both will start and run for about 5 minutes. But then the port engine will start making a loud hissing noise as if it is starving for fuel, and as the throttle opens all it gets is air and then runs rough and quits. Once the engine shuts down, it will not start for maybe an hour or two, but then will start and run beautifully again.

If the engine sits for 15 to 30 minutes, it will start and continue running with no problem. Only after about an hour to an hour and 1/2 does this problem happen.

Does anyone recognize this problem and have a solution?
Any help will be much appreciated.
Thanks.

If you have those stupid mechanical fuel pumps mounted to the sea pumps...pull them off and cap the hole...then throw those fuel pumps as far as youo can. Install electric fuel pumps like the Holley RED pump for each motor and this crap will stop. You fuel system is vapor locking with those mechanical fuel pumps.

Thanks. This sounds correct, I will have my mechanic look at it.

Search vapor lock 502 or VST.

This is a good one.

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

Vapor locking like was said.