I run the blue Holley pump, it is mounted about 1" above the tank. I have modified the pickup from stock to 1/2". The pump is wired off a relay, with a low oil pressure cut off switch. This has worked great for quite some time.

Kenny, I hear ya on the smallest hose restriction! Mine was changed over to the 1/2" lines, with the anti siphon valve removed for even less restriction, and fuel/water separator upgraded to high flow. I'm feeding a 1050 dominator on top of a blower using only the mechanical pump. Always have 7psi pressure. Actually, my gauge at the carb shows 9 at idle. I added a regulator to set at 7psi. Plus needed more red anodized chit!

Now my thought/question.............

Okay, now we all have these big unrestricted 1/2" fuel lines, up graded to the high flow fuel water separator, removed anti siphon valves, some with electric fuel pumps in addition to the mechanical pumps..............and feeding what..........2, maybe 4 fuel needle & seats that are only .125" ID in dia each (and that is erroring on the larger side, .093 more realistic). That's not counting the restriction from the needle itself, so actually even less!!! And to top it off, that is thinking that the needles are fully open all the time. Has anyone ACTUALLY have some 1st hand experience on any improvements by upgrading the fuel lines to 1/2"?

I'm all ears on this as it has never made since to my simple little mind.

Thanks

The HV carter is rated at 6-8 psi and 120 GPH. Mine reads 8 psi at the carb and 6 on the dash. Because of some other fuel problems I had I have a holley elect. pump as a feeder pump.

US1Fountain;

I personally don't have any first hand experience to talk about, but this is my opinion anyway.

I understand your thoughts. If you do the math it agrees with your theory.
1/2'" fuel line = .19625 square inches.
.125 needle and seat=.01226 square inches.

Say you have a single carb. running .125 needle and seats. Thats only .02452 square inches ( the area of both the needle and seats) of area where fuel can flow into both carb. bowls. Why do we need .19625 square inches ( the 1/2" line) of fuel to feed only .02452 ( the 2 needle and seats)???
The only reason I can figure is to make sure that there is enough fuel volume at the needle and seats so the jets don't suck the bowls dry.
When your motor is spinning at 5000 rpm and under a load, the fuel is being sucked in, not pushed in. There is no fuel pressure in a carb. bowl. So fuel is not pushed into the motor, the motor draws it in by vacuum. The fuel pressure is in the lines before the needle and seats forcing fuel into the bowls. I would imagine that is the reason why the small hole of the needle and seat can feed the larger combined holes of both of the jets in a metering block. BUT, you need the pressure to force the fuel pass the needle along with having enough of a volume of fuel so the bowls don't run dry.
So, what the hell am I trying to say?? I think that you need a larger diameter fuel line to feed the motor. Especially for a worked motor. It is better to have too much fuel at the needle and seat than too little. The motor will only use what you allow it to use by your regulating the jet size anyway.
I am not saying that you don't think that a 1/2" line is a good idea, I am only trying to convey my theory on this.

WOW THIS IS GETTING DEEP.
DO YOU REALLY NEED 1/2 FUEL LINE.LOOK AT FUEL INJ. MOTORS THEY HAVE 5/16 FUEL RAILS I THINK? BUT THEY RUN 40 PSI PRESS.

I RUN 2 HOLLEY MARINE BLACK PUMPS ON MY RIDE-THEY ARE FED SEPERATELY WITH 1/2 LINES(#8) THEN TEE INTO SINGLE #10 LINE THAT FEED MY B/G 4 PORT REG (NO RETURN)NO PROBLEMS AS OF YET(KNOCK ON WOOD)--YOU COULD JUST CATCH A GLIMPSE OF THEM IN THE PICTURE SECTION--UNDER HEART OF MY CAT....

I don't think that you can compare a fuel injection system to a carb. As I said in my previous post, in a carb. you are relying on the vacuum to suck fuel down a carb. venturi. I don't know how many inches of hg that an engine creates through the venturis' but I would venture to say that it doesn't equate to 40 P.S.I. as in an injection system. In injection, you have all that fuel pressure built up sitting at the pintle waiting for the ecu to fire the injector coil, when it does the fuel will be forced down into the intake very near the head. Not only is there alot of pressure here, ( 40 psi as compared to 6psi at the carb needle and seat) the amount of fuel is regulated by the ecu, and is squirted nearly directly into the head, as opposed what ever falls down through the carb venturiis' , mixes under the carb, then drawn down the intake, through the head and finally into the combustion chamber.
In efi, the fact that the fuel is shot in at the end of the intake manifold would definetly affect the characteristics of the air flow in the intake due to the air being dry for almost the entire run. This along with the fact that the fuel is sprayed in and its' mixture more closely regulated by the e.c.u., would promote better atomization of fuel. I feel that these 2 facts are part of what allows an e.f.i. system to run leaner and still be safe.
How the hell did I get onto this?
It seems that I have gone off on a tangent somewhere back after my first sentence.
Oh well, for what it's worth my .02 says that you can get away with a smaller line in an injected motor just because of the nature of its' design.

I didn't know this thread was going on before I started another one. I would be interested in your comments on my fuel pump dilemma.



[URL=http://www.offshoreonly.com/forum/showthread.php?s=&postid=340332#post340332]

I too went throught the delemma (sp) of wondering how I would get a electric pump to work above the tank. I have used a mallory 140 and now a 250 with return and have had no problems. In about a second or two, the pump builds pressure, meaning, it obviously sucked the fuel the 12-15" from my tank (vertical distance only) and pressurized it. I did however have problems with a deadhead regulator sticking after a wot run. Return style works great.

THANKS BRAD! I've been stressing over my installation, for some time now! I finally decided to just try it-if it didn't work, I'd replumb. In your application, are you running a coarse prefilter and a check valve? I was thinking of adding these to my setup.