Last year, my first year in this boat, the engine would vaporlock and run hot at mid-high rpm. Come to find out Ive only 29-31psi fuel pressure. Im istalling a new pump, regulator and gauge so what my pressure be set to? Engine is a stock 96 502 mag.

I'm pretty sure I've seen 43 psi listed as what you should have

Wow. If that's the case I'm WAAAAY low.

Double. Check that but I thought they said 38 to 43

+1. My 502 tested at 38psi last spring.

Start on page 5C-60, in the merc manual #16,

small amount of fuel leakage
that may occur when installing the gauge.
Ignition ON, pump pressure should be 34-38 PSI
(234-262 kPa). This pressure is controlled by
spring pressure within the regulator assembly.

Pretty much says under 34 psi and the system will run lean, under 24 psi the engine wont idle,

Test:
Pressure less than 34 PSI (234 kPa) falls into two
areas:
• Regulated pressure less than 34 PSI (234 kPa).
The system will be running lean. Also, hard starting
when cold and overall poor performance will
be noticed.
• Restricted flow causing pressure drop. Normally,
an engine with a fuel pressure of less than 24 PSI
(165 kPa) at idle will not be driveable. However,
if the pressure drop occurs only while underway,
the engine will surge then stop running as pressure
begins to drop rapidly. This is most likely
caused by a restricted fuel line or plugged water
separating fuel filter.
2. Restricting the fuel return line (Using Special Tool
- Shut-Off Valve) allows the fuel pressure to build
above regulated pressure. With battery voltage
applied to the fuel pump, pressure should rise to
60 PSI (414 kPa) as the fuel return hose is gradually
pinched.
NOTE: Do not allow fuel pressure to exceed 60 PSI
(414 kPa); damage to the pressure regulator may result.
3. This test determines if the high fuel pressure is
due to a restricted fuel return line or a pressure
regulator problem.

just to clarify what people are saying, EFI or carb??
Makes a huge difference

EFI.

Thanks 92NSX!

VST systems 34-38PSI

Manual says 37psi running.