Rodbolt 17 please help!!

[dorado42]

OK the latest report....borrowed a hand held vacum gauge (the ones you can use to bleed brakes). I started with fuel pick ups and antisiphon connected to a piece of 6 inch hose, applied 20 mm/hg (I know boat does not create that much vacum) to see if they would hold the vacum. Left it alone for an hour, no change!!! AIRTIGHT right. I did the same thing with main fuel line (the one foamed into side of boat) after leaving over night dropped to 18.5 mm/hg. I do not think that drop is significant for overnight. I did hook a clear fuel line up to the tank and pump gas into a five gallon bucket and could see small air bubbles in the clear line. Can the air bubbles be coming from the small ball inside the antisiphon valve? Can the pick up be sucking air when the pump is drawing it and not still hold a vacum? Anyone have any suggestions.....boat runs great on 6 inch piece of hose in portable tank, but do not have deck space for 55 gallon drums (LOL)(JUST KIDDING)

[dorado42]

CORRECTION TO PREVIOUS POST: Can the pick up be sucking air when the pump is drawing it and STILL BE ABLE TO hold a vacum on the gauge?

[MatthewCide]

newbie!

Just wanted to drop in and say hi, new to this forum and looking to pick up some tips.

[rodbolt17]

nope.
all the fuel pump is is a vacuum pump.

[dorado42]

Ok, the saga continues...i used a bleeder vacum pump, like the kind to bleed brakes....i vacum tested the pickup tube, antisiphon valve, main fuel line and they held vacum without leaking. I checked the racor system and FMM system no leaks. I hooked the entire system back together and pumped the system full. So far their seems to be no loose of vacum. It does seem that when the primer ball is pumped the antisiphon valve introduces small air bubbles into the fuel line, I can hear the ball vibrating when the ball is pumped. Is this normal? Is it possible the air from the antisiphon valve is building in the system after a while, or does the vst help eliminate the air?

[rodbolt17]

that ball and spring in the anti siphon valve is doing what its supposed to do.
if you suspect a fuel supply issue its to easy to use an electric pump and a vacuum guage to spot air leaks or restrictions.
hook up a pump drawing from the lift pump side of the engine fuel filter.
run the outlet hose back to the tank fill tube.

now using your FMM turn on the pump.
use vise grips or a valve and throttle the fuel flow to about 25 gallons per hour.
for a 2.6L you should see lass than 4"Hg on the vacuum guage.
3.1L less than 6"

now we know we are drawing through an anti siphon valve.
that should drop 1.5 to 3"Hg depending on the valve.
a clean fuel water separator will drop about 1"Hg.
the engine fuel cup will drop .5-1"Hg.

so we should have at least a 2-3" Hg drop and no more than 6"Hg for a 3.1L or 4"Hg for a 2.6L.

there is some good reading on anti-siphon valves and the various head pressures required.
while I have never seen one marked not all valves break at the same vacuum.
vacuum break spring will be determined by the static head pressure of the fuel line at its lowest point below the top of the tank.

[dorado42]

Ok..still pulling my hair out on this fuel problem. I ran a new fuel line with clear hose to be able to " see" what is going on. The supply line is full of gas and looks Ok...when the problem started we put a small piece of hose into a portable tank and motor ran fine....put it on fuel line "old one" and problem reoccurred. I replaced fuel line with the clear line and motors ran fine....thought i had found the problem....BUT....when i got boat back to dock, i left the boat idling while i backed the trailer in the water. When i went to load the boat the port engine had died and would not stay running for me load the boat....acted the same way...starts but as soon as i apply throttle it will throttle up and the loose power, REALLY FRUSTRATING. Question: If fuel line is new, antisiphon good, primer ball good, all hose clamps tight, motor runs good on portable tank, what else can it be? The racor and FMM systems have been vacuum tested and do not have any problem.

[99yam40]

Run the test Rodbolt listed in his last post to see what it is pulling or take to a shop that can

[dorado42]

Ok I ran tHe test as rodbolt17 recommended...THANK YOU very much it is soooo much easier to work on boat on trailer than the water. I ran an extra low pressure pump to the way rodbolt17 explained but my FMM was showing about 38 gph..instead of the recommended 25 gph. I tried squeezing line with vice scripe pliers and it did reduce GPH but increased vacum. So with 38GPH here is what I found: I ran a clear hose from the tank (with pick up and anti-siphon) in line to the transom where it attaches to fitting going thru hull to line going to primer ball to fuel line going to element, the gauge was reading 7 mm/hg. I understand it should be 1-2 mm for anti-siphon and 1 mm for primer and 1mm for engine element, so where is the other 3-4 mm restriction coming from.

[rodbolt17]

I NEVER EVER mentioned mmHg.
in my opinion the metric system is a waste of my time.

try throttling the OUTLET side of the pump.

the max for your motor, between the lift pump inlet and the liquid in the tank , is 6"Hg
I use a length of hose and simply return the oulet fuel back to the fuel tank.

if the vacuum is to high start backing up to various inlet and outlets until the restriction is found.

you should be able to flow 25GPH at 4"Hg or less.

[dorado42]

Yes rodbolt17 that is what i did ran the pump from outlet side of engine fuel element and found 7hg there with a clear hose going from fuel tank to engine (no racor no fmm)...so i thought the theory was 1-2 hg for anti-siphon, 1 hg for primer and 1 hg for engine fuel element....so at worst is 4 hg (2 for antisiphon,1 for primer and one for engine element) where would the other 3 hg be restricted from.

[dorado42]

Rodbolt17 is it ok that i conducted these test with NO LOAD on motors, motors not running at all and also does it matter that fmm gauge was reading 38 GPH (instead of recommended 25 GPH)...thanks for your time, patience and expertise

[rodbolt17]

yes, many things MATTER.

one is the difference between " Hg and mm HG.
the former is inches of mercury and the latter is millimeters Hg.

through a given hose run and the various fittings the difference in system vacuum between 38 GPH and 25 GPH can be considerable.

rerun the test,throttle the outlet side of your electric pump to about 25 GPH.
measure the fuel system vacuum between the outlet side of the engine fuel filter and the inlet to your electric pump.

[99yam40]

Conversion table shows
1 inch HG = 25.4 MM HG at 0 Deg C

So it is a big difference

Make sure what scale you are measuring in

[dorado42]

I checked the gauge i was using yesterday and it is definitely inches of hg NOT mm/hg. So if the motors are not running how do you recommend i " throttle back" my remote pump to 25 gph instead of 38 gph. I tried squeezing with vice scripes but eventhough it slowed flow to ~26 gph it increased the vacum due to the restriction of vice scripe