I have a slightly built 502mpi that is getting vapor lock. It fires up great runs hard for about 1 mile and then starts vapor locking. I can unscrew the fuel filter a bit and tighten it back up and it's good to go until you shut it off for a while and does the same thing when you start back off. Any help????

vst tank or cool fuel?

vst ???

Isnt there a factory kit to stop the vapor lock issues?

clean the screens in the bottom of the vst tanks, and i run my bilge blower from the time i leave dock until i put boat away to help pump heat out of engine compartment. i also only run 93 octane.

the first thing i would do is get some decent ventalation thru the engine compartment... think about it... vapor lock occurs when the fuel gets hot enough to boil. that happens when the lines and intake manifold and all the rest get hot enough to cook on. if you get the engine compartment temps down not only will the motor run a lot better but your problem may well disappear

There is a booster pump kit designed for the cool fuel systems.
It doesn't work with VST systems.

The VST motors have a small square tank on top of the engine that has a pump in it to feed the fuel rail, on the right rear mounted to the intake.

The last VST motors made had a small fiberglass shield mounted between the exhaust and the mechanical fuel pump, this can help and is easy to duplicate. You can also run the return line from the VST tank back into the fuel tank which will help tremendously. Finally if you do vapor lock, dip a cup of ice water from the cooler and pour it on the mechanical fuel pump mounted on the water pump, that's where the lock occurs.

I don't think this is a vst, no square tank on top. The fuel filter is mounted on the left side facing the motor right behind the belt near the front and the lines run under the motor to the right side under the engine mount. What vents are they talking about being clogged. I can put the boat in drive about a mile and then it happens is that long enough for it to get hot enough? I can unscrew the fuel filter just a bit and tighten back up and its good to go until I shut it off for a while and then the same thing once I start back off again..

What are these and where.