Fuel pump mystery issue continued

[joe_db]

Some of you may recall I have had a very frustrating fuel pressure issue. Over time, the fuel pressure slowly falls to 0. If I kick on the second pump, it works for a bit and then falls back to 0. Even at 0 the engine still runs, so fuel is - slowly - making it to the engine in enough quantity so it never misses a beat. I did an experiment and rigged a return and that would bring the pressure back up if it was valved off to not be wide open. I never did rig it permanently because I didn't want to have gas flowing like that if I could help it AND the engine seems to run fine anyway.
So - this spring I decided to get to the bottom of this. I rigged the pumps in parallel instead of in series. Now the issue is WORSE. The pressure is lower and it falls off faster
Hmm........what to try next. I have an old pump and a new one. The fuel line to the engine comes from the old one and the new one Tees into it. I pinched off the fuel line from the new one, isolating it more or less depending on how hard I pinched, and the fuel pressure jumped up to 2 PSI. So now I am about to hit myself with a socket wrench! Could it be all along the "new" pump has some valve/leak issue that bleeds off pressure? I am going to just get rid of the thing and try the old pump all alone and see how that does. I really hate it when my ideas to have more reliability end up doing the exact opposite

NEXT: I am thinking there are better pumps than the old can pumps.
See this :

https://www.pegasusautoracing.com/productdetails.asp?RecID=7550

And this:

http://www.facet-purolator.com/Facet_%20Cube%20Fuel%20Pumps%20_%20Facet%20Purolator%20(Original).pdf

The 40178 pump has dry lift of 36 inches, 2-3.5 PSI, and has both a check valve and a positive shutoff. When you cut power, it internally shuts the valves off These would work perfectly in parallel if you wanted more than one.

[lat 64]

I am currently using one of those cube pumps, but I cannot recommend it yet. I have priming problems that just won't go away. I think there is a problem that it just won't prime with a stuck float valve. But like so many things, I'm probably over thinking this.

Russ

[joe_db]

Try taking the hose off the carb and adding a section back to the tank with a squeeze bulb (temporarily!). That should get it unless you have a clog or an air leak.

I am currently using one of those cube pumps, but I cannot recommend it yet. I have priming problems that just won't go away. I think there is a problem that it just won't prime with a stuck float valve. But like so many things, I'm probably over thinking this.

Russ

[lat 64]

I'm suspicious of an air leak. No time to get to the boat until april. This will have to wait.

[Dave Neptune]

Ain't right

Joe, you say the engine is running fine even at zero preassure. That tells me the gage is failing to read even when enough preassure to feed the carb is present (1 1/2~2 psi) and not showing.
There should be absolutely no need for 2 pumps to deliver enough fuel to an A-4 unless you had the engine on the deck and the tank in the keel!

Are/is the pump(s) still ticking when zero is reached and the engine is purring along? When you say running do you mean idle, slow or cruise speed?

Russ & Joe to confirm that the needle is indeed stuck is problematic in itself because checking often shakes them loose. I really doubt they are sticking closed and if you loosen the fuel line that goes into the carb at the end away from the carb (IE no banging or jostling the carb to shake the needle loose if stuck) you can blow through it. If you can blow through it's not stuck CLOSED. I suggest you drain the carb first, if there is still fuel in the bowl it could be enough to hold the needle closed. Needles "usually" stick open and cause flooding not the other way around, although it is possible.

The fuel system should be very simple ~~ tank~main filter~pump (electric or mech.)~gage~carb. A "polishing" filter can be installed between the pump and the gage. The gage should be the last in the line so you know what the carb "sees".

Dave Neptune

[joe_db]

I am sure the pressure isn't absolutely 0. Likely 1/4 PSI and the gauge won't move for that little. It does run fine even at full throttle. I even found out I can run a full open bypass and enough gas trickles down to the carb anyway to run the engine when I had a temporary bypass run. We use all of what - 1 GPH?
Anyway, I have 2 pumps because I had one and the new engine had one too. Clever me decides to hook them both up in case one dies and I *think* all I did was combine one with issues with a good one to make a 1/2 working setup. I'll report back after I get what I think is the defective one out of the circuit.

[hanleyclifford]

I've been running the same pair of these in parallel now for 20 years. FWIW http://www.advrider.com/forums/showthread.php?t=728034

[romantic comedy]

I would like to see how you have them in parellel. Are you using a check valve?

It seems that the gauge might be suspect.

[joe_db]

Today I tested just one pump with the other one blocked off. Pressure was 4 PSI at startup and drifted down to about 1.8-2.0 PSI after one hour. MUCH better that the 2 in parallel, which hit 0 PSI after about 10 minutes. The 2 in series drifted down to 0 in about 30 minutes. So...........looks like the one pump is best.