Need advice on low pressure fuel pump psi?

[ronreece]

So the little vent hose coming off the top of the vapor tank is leaking out fuel into the intake silencer and ultimately out of the engine.
I have the vapor tank out of the engine and assume it's either the float (which appears fine and has no fuel inside it), the float adjustment (which appears fine also), or the needle valve isn't seating for whatever reason (and I'm betting that's probably it).
I have a new needle valve assembly and o-ring, but before I remove the old valve, I wanted to check it.
I was planning on pressurizing the low fuel pump side hose (after pushing the float up to the normal level that it would ride in the tank) and see if the valve leaks.
My question is, what psi should be applied to verify the needle valve is seating properly and not leaking?
Any help would be appreciated!

[rodbolt17]

without a model number? somewhere between 4 and 10 PSI.

VST tanks have been used on two and four stroke engines with mechanical and electric pumps since at least 1995.

[ronreece]

Guess I forgot an important bit of info
The engine is a 2004 Yamaha F115 four stroke.

[rodbolt17]

you should see about 6 PSI, single mechanical diaphragm pump for low pressure.

my bet is a leaking VST needle or a loose needle seat or a bad needle seat oring.

[ronreece]

Yep. I replaced the needle seat assembly and o-ring, pressured it up to about 10 psi, and no leakage.
Good to go.
Thanks.