28Eliminator

Pismo10, you are correct on the lower one. The top one is coming right out of the fuel pump section. Are you having this vapor lock problem? If so, pull the top off and the diaphram and note what side the spring is on. Also bigblueheaven,s vst was the old style which is supossed to be on top. It is the first link I posted on the second page of this thread.

pocketchange22 has probably the best way to eliminate the problem all together, I just wasn't ready to throw another $1000 at mine as I had just bought the boat, installed a whipple and bought a new Bravo1. The banker (wife) stopped the spending.


bigblueheaven, I'm glad it fixed your problem. If more people would read this, they would save themselves a lot of time troubleshooting this problem. The easiest test is to just pull the inspection plug off the top of of the tank and see if the problem goes away.

Pismo10

I have the newer style VST with the spring on the correct side. I have never had a vapor lock problem yet but it seems common and I want to not be surprised. I have dealt with it on other vehicles and realize how troublesome it can be. Pulling the inspection plug will get me home, then I will engineer a fix if and only if this problem ever arises. So far so good so I am just learning for now.

Pocket change's solution sounds final but $1000 at least so I will wait for the problem to arise.

28Eliminator

I don't think you will ever have a problem then, unless something quits working or gets plugged up. Once I change my spring to the correct side my main problem went away for the most part. The only issue I have sometimes is when it's really hot out and the boat's been sitting for a while. When I start it up, it will start for a few seconds and die, maybe once or twice. Not sure if it's the vst is causing this problem or not though. I really should troubleshoot this with my fuel pressure gauge, because it is annoying.
I should take my own advise and pull the plug the next time it happens to see what the results are, but you never really know when it's going to happen.

go propless

Well Before you blow all of the money on new parts,electric fuel pumps and the 3 steps the mecuriser bull. tells you to do. just reroute your fuel lines. The factory line run from the furl pump up the front of eash motor then cross the top of the motor and into the vst and it is all steel line ****ting right on top of a hot motor. It is going to vapor lock. I rerouted my furl line on my 97 sonic with twin 502MPI mags and the problem is fixed for around $50.00 Hope this helps

Pismo10

I would love to get rid of the pulley fuel pump, the VST, have easily adjustable fuel pressure. A much simpler, better, more flexible system. So there are more benefits than just getting rid of the vapor lock. But I still won't do it until I have a problem.

jms5051

I think I am having vapor locking problems also. I have twin 1997 502s but the only thing confusing me is one of my engines is acting up but the other one runs great. After it has been running for anywhere from 10 to 20 minutes the one engine starts acting like it is running out of fuel, skipping, sputtering and sucking air really bad then cuts off. I tried opening the vent on the VST and this seems to clear things up for a bit but it eventually does it again. I pulled the vst and the spring is located on the bottom of the diaphram. I am still confused as to whether this is right or not. If this is wrong, does this mean the one on the other engine is backwards too? If I swap it around, will there be any negative impacts if this isn't correct? Any help would be great. Thanks.

28Eliminator

If it was running good for a long time then it probably is not assembled incorrrectly. Several things can cause vapor lock issues. I think this setup is why Merc decided to reengineer the setup for newer setups. The diaghram could be bad, or the screen in the bottom could be getting plugged, causing the starvation. The small vent hose that hooks to the top has to be vented and not plugged, going to the manifold, or it will not evacuate the VST tank pressure; or is there a vent hose next to the vent plug? Is it this style, with a vent tube next to the plug? if so the spring is on the correct side.
http://www.mercruiserparts.com/Show_...SEPARATOR+TANK

I will try and help if you can give some more feedback.

28Eliminator

I just pulled my manual, and the proper location for the spring is on top, if the vent port is right in the middle, infront of the inspection plug and point towards the intake. So the big question is, do you have the vent port there or not. If so change the spring location and your problem should go away.

Pokher Ace

Does anybody have a picture of where the spring should be placed?

Pismo10

This thread post #17