vst vapor locking?

how do you stop vapor lock in a vst type injection system?the motor is a 502 mag,efi.it uses the early type vst.this is a 1994 motor.i rebuilt the motor last year to stock spec.i did add roller rockers and i had the injectors cleaned and flowed.new mech. pump.the boat always ran rough when idling,but i can deal w/that.now when i run hard for a hour or so and stop for longer than a half hour,the engine will start,idle ok,then go to get on plain,the motor starts to vapor lock.high pressure pump reading on remote gage is about 37psi.it will gage,spit a few times and clear up.wtf?vapor lock?

The vapor lock occurs in the mechanical fuel pump on the engine. Merc fixed it by going to the cool fuel setup. It is fairly easy to convert the system over and the parts are readily available. Basically you switch to an electric fuel pump and a water cooled heat exchanger in water hose from the transom.

What about converting to serpentine as well? The old 502 mpi's are v belt and cool fuels are serpentine. I have one of each in my boat and would like to convert

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Originally Posted by bcfountain

how do you stop vapor lock in a vst type injection system?the motor is a 502 mag,efi.it uses the early type vst.this is a 1994 motor.i rebuilt the motor last year to stock spec.i did add roller rockers and i had the injectors cleaned and flowed.new mech. pump.the boat always ran rough when idling,but i can deal w/that.now when i run hard for a hour or so and stop for longer than a half hour,the engine will start,idle ok,then go to get on plain,the motor starts to vapor lock.high pressure pump reading on remote gage is about 37psi.it will gage,spit a few times and clear up.wtf?vapor lock?

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I would think if it vapor locked it wouldn't start. The rough idle and problem after sitting makes my suspect a water leak in the exhaust. What kind do you have. Did you check your exhaust during rebuild?