HiPerf2000

iTrader: (2)

i did a search on threads that are VST related. They say to check the diaphram for a possible leak is to put a clear hose in place of the vent hose....and you will see fuel flowing though.

question......can i do this with the boat running on the trailer? will it happen at all RPM's?

i have the hose off and am picking up a clear hose later and will give it a try tonight.


Is there anything else that is pretty simple to check while i am back there tonight??

RonS

It will show up when your at idle, also because the raw fuel dumps int #8 cylinder you will be able to smell the raw gas coming out of the exhaust.

HiPerf2000

iTrader: (2)

Thanks RonS.

Also, could a stuck open needle/seat valve cause excessive fuel usage?

What do i need to take apart on the VST to get to the needle/seat ??

Dave1972

The VST is actually very easy to take apart (except for the merc thread lock). I would remove the lines and take the tank off the mounting and look at it on the bench. Be sure to mark which lines go where (direction of flow) as they are the same size. From there just take the phillips-head screws off the top. Be careful not to damage the rubber-o-ring and you can re-use it. Is a good time to clean the pre-filter in the bottom of the VST tank (attached to high-pressure pump).

HiPerf2000

iTrader: (2)

Thanks Dave,

That brings up another question....i just had the top end of this motor apart, and now that it's back together it goes through 2 times more fuel than the other motor. What would happen if i switched the lines on the VST pump when i re-assembled? would it even run?

Dave1972

I don't think it would run for long if you switched the lines around. Not sure why you would be going through so much fuel. Have you checked the plugs to see if they are black/dark indicating rich condition? How does it run at all RPMs? What did you change on the "top end"? I had the opposite problem after rebuild and the screen/filter/pickup in the VST tank was clogged and it would only run at idle....the filter was so clogged I wasn't getting fuel. If you do pull plugs, be sure to pull all of them to make sure they are consistent. #8 is the one I would be careful of as mentioned before as there is no fuel return on the VST. Keep us posted.

HiPerf2000

iTrader: (2)

Haven't checked the plugs yet but that side of the transom (twin motors) gets darker than normal. I put the diag tool on the computer and showed no codes.

The boat does not run bad at any RPM's (which is the wierd part). I tore down the top end because i had a one time water ingestion problem......which ended up being a "Y" pipe flapper Didn't realize this until we found nothing wrong with the heads or gaskets when we pulled them. I did put exhaust valves in it while i had them off because they were looking corroded.

I will first check for a diaphram problem tonight with the clear hose, then i'll pull the assembly off.

HiPerf2000

iTrader: (2)

UPDATE.

checked for a leaking diaphram tonight with the clear hose, and found no problems there.

Would the needle and seat being stuck partially open cause a rich condition?

I also plan on checking the fuel pressure. how much should i get at idle? or other RPM ranges?

Dave1972

I believe that Merc wants you to have around 37psi at the rail and I believe it should be pretty consistent. Not sure about the needle/seat being stuck open and causing a rich condition. Keep us posted on your progress.

RonS

You may want to check that you are getting proper voltage to the temp sender, you said you had the motor apart so check all your pin connectors and make sure that there are no wires pulled out. If the temp sender is not working correctly the ecm may be putting the motor in the cold start enrich mode causing the excessively rich condition