28Eliminator

Remove VSTs and install a high pressure pump and be done with it.[/QUOTE]

+1
Even though I had way better success once I fixed the VST spring location, I still had times of hard start during a heat soak period. I eventually replaced most of the fuel system hoses, water seperator, Aeromotive pump and regulator and never have a problem.
Now on to your problem and understanding, the diaphram valve should be closed when the motor is off to prevent gas fumes from entering the bilge, thus preventing a possible explosion. Once the engine starts, the diaphram should open to relieve the built up pressure in the VST tank. These pictures we have posted don't show the actual vacuum path inside the VST. Follow the lines within the top housing and the diaphram housing to see where the actual vacuum would route through to pull against the spring. Based on the older style, which I don't have laying around, and the diagrams it looks like your spring should be on the top of the diaphram, so I would change it and see how it does.
The 3 VST tanks I have here are the newer style, thus most of my information is based on that and not the older style, but everything I have seen shows that your spring should be located on top of the diaphram. Good luck and happy boating!

Pismo10

That does seem to be the ultimate final solution to the VST problem.

Knotcrazy

Thank you 28Eliminator.

My original plan this winter was to replace the fuel pumps with a couple or Aeromotives and be done with it. But while researching the electric pumps in general I seemed to come across a pretty consistent theme: The electric pumps are only good for a couple of years and then rebuild or replace. I'm not really interested in spending over $1000 for a couple of pumps and regulators if the pumps aren't going to last more than 100hrs.

How many hours are on your Aeromotive pumps?

Cole2534

You dont need to use the A1000 pump, I'm using their smallest pump, #11109 IIRC. All in all, im in my retrofit for probably $450.

Capt.Yar

Hi guys. I'm back with vapor lock problem again.
So few months have passed since I fixed my VST tank after which everything was perfect. I put 120h with no problem and now same problem occurs. It looks like Florida hot summer temperatures are boiling the gas again.
My question is where this time? It's not in the VST. I unscrewed the plug and there was no high pressure gasses escaping.
Engine always starts after cooling down 1 -2 hours after.
Last time(before VST modification) engine started ran for 3-5min and dyed after burning the fuel from VST tank. Then when it cooled down it started again.
This time after heat soak period the engine won't even start. I can turn and turn it till the batteries are dead. It starts eventually once it's cooled.
What should I do this time ?

silent lucidity

I've posted many times on this subject as I chased this issue trying everything people offered.. Got tired of the problem. Gutted mech. Pump and VST's.. Changed to single aeromotive pumps with new bypass regulators and no more issues. This cleaned up engine compartments, simplified process and less parts..also my engines seem to run soooooo much better. Mid level punch was awesome...
Search Vapor lock on here..there's tons of info about...when you get tired of trying things you'll bight the bullet and make the change,,, it's not cheap but not hard to do either. Good luck

28Eliminator

+1, exactly what I did and never have a problem.
You need to start by checking fuel pressure. I would guess that one of the fuel pumps maybe getting weak. Ethanol kills any older mechanical fuel pumps and maybe even some newer ones. My brother rebuilt his over the winter and talked to a tech guy (holley or carter can't remember) to get the right rebuild kit, and the guy said the ethanol is what was killing all the older mech fuel pumps. And my brothers fuel pump wasn't that old, but who knows how long it was sitting on a warehouse shelf.

Capt.Yar

Is it possible that there's no return line from the fuel rail on my engine( 7.4 LX EFI/MP) or I just can't find it?

Capt.Yar

I've decided to get rid of mech.pump and vst. Is this correct order should I assemble it ? Please correct me if I'm wrong.
Fuel tank --> aeromotive pump --> fuel filter --> fuel pressure regulator --> fuel rail.
What kind of fuel pressure regulator should I get? Link would help a lot.
What exactly should I do with mech.fuel pump?

F-2 Speedy

put the filter in front of the pump and get a EFI bypass regulator