Fuel Pumps Questions.
 

I have Mercury Racing engines 600SC's, I am starting to be very annoyed about the mechanical fuel pumps on my mills.

I have put new ones on both engines this spring when i started using the boat and I am not satisfied with these things... I am constantly looking at my fuel pressure and have become very tentative with fuel pressures that do not seem to be consistent at all. Why are those things so freaking flaky as to performing consistently.

Anyway I am now considering seriously electric fuel pumps with regulators.

I would like input from engine builders and knowledgeable fellow OSO'ers as I have found this is a reliable forum to get reasonable suggestions.

Thanks for your input. And have a peak at this while thinking of what set-up could put my mind at ease with the pressure on my twins!

G.L. Harvie

Re: Fuel Pumps Questions.
 

Sorry I posted this in the wrong section.

If God is watching maybe you could move it to the Tech section. Thank you.

Re: Fuel Pumps Questions.
 

hey . . as long as you post it like that . . have at it :D :D :D

Re: Fuel Pumps Questions.
 

as a matter of fact i think that any "off general discussion" post must be acompanied by a photo of a scantly clad female (sorry women of OSO, start a new thread :D :p ) :D :drink:

Re: Fuel Pumps Questions.
 

GLH,

I know where you're coming from. I think I've bought every mechanical pump on the market, including the 170 gph Hardin Marine pump and my fuel pressure would still drop to 3lbs after a while at wide open. I finally decided to go with electric pumps and have been able to forget about low fuel pressure altogether. I've been running the Holley "Black" electric pumps this season. With the regulators adjusted to 9lbs at idle, I'm at 6lbs under boost.

...are you going to Miami in Feb.? :drink: :eek: :D

Kurt

Re: Fuel Pumps Questions.
 

same problem as glh, im always worried about my pressure. i have to get a correct pressure reading, not even sure the gauges are correct. kurt did you change the pumps yourself??? dave

Re: Fuel Pumps Questions.
 

Many people have had problems with the electric pumps burning up. Some have burned a pump up with in hours of installing it. The problem comes from them having to lift the fuel and then being dead headed. I'm running a pair of Mallory 140 marine pumps. When I first installed them, I had the pumps dead headed. These pumps had a internal bypass that was supposed to eliminate the need for one. I decided to add the bypass to prolong the life of the pump. There was a noticeable difference in the sound of the pump after the return was installed. The pump was definitely not working as hard. That was 2 seasons ago. I now have about 50 hours on the engine (about 25 on each pump) and they are needing to be rebuilt. When the tanks get below 1/2 the pumps are no longer able to lift the fuel and the pressure quickly drops to zero. As nice as the electrics may be, I'm thinking that the real solution still resides in the old mechanical pump. Frankly, I don't think the Hardin pump is a very good one. I'm not sure if Edelbrock offers a marine fuel pump, but they would be my first choice. You should be able to convert the standard 6 valve street pump to marine duty pretty easily. You just need to remove the hose bung from your current Hardin pump and install it into the new one. I believe that the hole would be 1/8" pipe.

Re: Fuel Pumps Questions.
 

You might try a Merc 900sc mech.I have had pretty good luck it. However I now run a 14 psi BG with a regulator and a return line. It is cheaper and I get NO fluctuation. Just be sure to run to return line, you can plumb is without one but you will still get fluctuations. Forget the electric.There are problems with being coast guard approved, and fire hazards which brings up the insurance issues if you ever have a problem. I have run over 1000HP with no pressure drop a all. Just my experiences.

Re: Fuel Pumps Questions.
 

do you have one way check valves in your fuel system?

Re: Fuel Pumps Questions.
 

GLH,

Have you changed your fuel filters recently? I had a problem this summer with low fuel pressure that resolved immediately with fresh filters. Also, is the fuel line from the tank to the pump sufficient size to feed the pumps? With 600 H.P., you should be running at least AN -10 size supply line to the pumps.

I feed my 650 H.P. with AN -10 lines, Racor water separating fuel filters, Holley mech pumps, and a regulator just before the carb. Might want to check with Mike @ C.P. Performance. He has always been very helpful to me with advice on this topic.

Chris

Re: Fuel Pumps Questions.
 

Kurt,
Thanks for the input.

I can't make the Miami Boat Show my wife is due with our second son on the 15th of Feb... unless you supply me with a way to explain to her I need to be at a boat show while she gives birth!!!

Re: Fuel Pumps Questions.
 

Dave I have switch the senders around and the gauges around
, also I checked it with suplemental mechanical gauge and it still fluctuates.

Re: Fuel Pumps Questions.
 

Those were yanked out before I bought the boat last January.

I also have changed the fuel filters and changed pumps again for a minimal difference and then back to the same unreliability in pressures. Also this is only happening on one engine. Although while winterizing this weekend I noticed I have a very small leak on the pump that actually is working and holding pressure fine...

I love boating man!!!

Re: Fuel Pumps Questions.
 

Are the pumps mounted as low as possible?
I always thought they should be mounted at or below the bottom of the fuel tank. I say this because electric pumps are not good at pulling the fuel from the tank, but excellent at pushing it up to the carb. That's why EFI pumps are generally mounted in the tank. There are exceptions, but they are frame mounted and below the fuel tank.

Re: Fuel Pumps Questions.
 

The Mallory 140 pumps are great AS LONG AS YOU USE A RETURN REGULATOR. You should never deadhead an electric pump if you expect it to last. I have burned up 1 Mallory Comp140 and 2 Holley Red pumps by deadheading. Once I used the return regulator the Mallory lasted indefinitely. Now on the issue of low fuel pressure on the carbureted engine; I don’t see this as being a major problem. Your engines are eating up fuel and your mechanical pumps are doing the job of filling the bowls. If your fuel pressure were high on a mechanical pump carbureted engine then the case could be made that you lacked sufficient fuel flow. When do you have this higher pressure? You have it at idle when the carburetors needle & seat are closed, or you could have it because of an obstruction. If you’re maintaining 3-PSI on a carbureted engine under full throttle then things would seem normal to me.

If you want to use an electric pump then great. Make sure to mount a regulator as close to the carburetor inlet as possible, and make sure you use the return style. This will guarantee you have sufficient fuel flow to your inlet or inlets (Holley) However You will still notice that fuel pressure falls off. Remember just because your fuel pressure is higher DOES NOT necessarily mean you getting more fuel flow to the carburetor.

On EFI engines things are very different. All EFI fuel systems in production today use the return to tank delivery. The benefits of this are the increased pump life, a never-ending supply of cool fuel to the engine (reduced vapor lock) I could go on but will digress. You have to look at the fuel pressure very different on a port EFI engine. Injectors are solely responsible for atomizing fuel and do so in a very fine matter. It takes at least 25-PSI for the modern disc-type fuel injector to properly atomize fuel. When the demand for fuel increases (full throttle) the injector will have to atomize a greater amount of fuel per shot. Two things have to happen for this to take place. The opening duration for the injector (pulse width) has to be extended and the fuel pressure must be increased. This is why you see your fuel pressure jump up when ever you open your throttle. On most EFI systems the fuel pressure regulators are controled by manifold pressure. Under vacuum the fuel pressure is lower, with less or no vacuum the pressure is increased and in turbocharged the regulator is pressurized to further increase fuel pressure.

In my opinion electric fuel pumps are the way to go whether you are carbureted or injected. Mount the pump to where it will be gravity fed because forcing the pump to prime itself can significantly reduce its output.

Sorry for the length but I was bored today

Roby

Re: Fuel Pumps Questions.
 

Just a suggestion. start with the pick ups. most mechanics do not. for big power applications, it is necessary to have ample diameter. also check for the proper use of fittings, from there back. I have seen #10 lines coupled to, for example a -10male flare to a 1/4 or 3/8 pipe nipple on opposing end, whats the use, restrictive. I.D is very important to maintain through out fuel system. I have also installed secondary fuel system's, which under boost assist the primary system to maintain pressure. Activated by a manual switch, or a boost activated hop switch. The secondary system is tee-ed into the primary on the out side of the mechanical pump. Very important, you must use A 1 WAY VALVE, between the " tee " and the electric fuel pump of the secondary fuel system. Additionally both fuel systems have separate fuel water separator's, and pick ups, and use the same return to the tank.Outside of using a NOISY Weldon electric pump and reg, this system work's best and is very reliable. It is also a fail safe to make sure your getting home if the primary mechanical pump fail's. One last thing , pump's water sep's , must all be mounted as close to pick up height as possible, and never have descending/ ascending height fluctuations. Always ascending. Hope its a help

Re: Fuel Pumps Questions.
 

This system worked perfectly with the current lines (9lbs on idle and 5.5-6 lbs. WOT) installed for the first 40 hours something is messing with me here. Now one engine goes down to 3.5 lbs between 4100 to 4900 and goes back up to 5lbs passed 4900.

Thanks for the input keep it coming. Here is some more motivation from the home country.

Re: Fuel Pumps Questions.
 

Nice Toe

Re: Fuel Pumps Questions.
 

GL,
I think Phil L. worked on mine before I bought it and he said it has a sensor and it will shut down if fuel pressure drops. Wont solve your problem but I thought it was a good idea to have. JM

Re: Fuel Pumps Questions.
 

Hey GL
This pic can keep my fuel pressure from drops :D :D

Rick OSG

Re: Fuel Pumps Questions.
 

GLH,

I will try to post a pic of my set-up this weekend. I have a stainless manifold that is screwed into the stock pump that also allows me to plumb in an electric pump. They both work together so I never have a pressure or volume drop. I am running a Whipple and I am feeding a big 850 carb.

Dave

Re: Fuel Pumps Questions.
 

I had those changed too, it was not the culprit.
I hate to quote Clinton but "are you feeling my pain!" :D

Re: Fuel Pumps Questions.
 

I would like to see that Dave thank you. Where did you get the manifold?

BTW I'm feeding twin Holleys 700 CFM's per mills, and feeding is definitely the apropos term!

More motivation for the contributers, this is broadening my minimal knowledge thanks!

Re: Fuel Pumps Questions.
 

GLH-

I got the manifold from Dino at Teague marine. I will get you a pic by saturday night.

Re: Fuel Pumps Questions.
 

pick up's, pump's and dont forget to check your fuel tank nent's. Hey one sick glad, what kind of speeds are you running, and what props? i am just about done re-rigging an 04' glad , richie builtthe power originally, and this time out we upped the power to just over 750, by zul of course. the input would be appreciated.


the monsta

Re: Fuel Pumps Questions.
 

I changed those also.

More motivation....

Re: Fuel Pumps Questions.
 

The heartbeat of america!!

Re: Fuel Pumps Questions.
 

I have been through most of the mechanical fuels pumps with many of the posted hassles. This includes that new Holley mechanical 20 series. I found a great solution. The CV Products custom billet mechanical pump with the 7.5 lbs. spring holds 6 lbs.+ steady at 6800 RPM on 780 hp. This pump eliminates the need for re-rigging, fuel pump auto shut off requirements, fuel returns or pressure regulators. I tapped the top of the CV pump and installed a barbed fitting to provide for an over flow to the carb.
Downside? It is a little pricey, but not as costly as the alternatives.

Re: Fuel Pumps Questions.
 

GLH:: I have the same setup from the factory,,, Stock Merc 600sc 1997 year.... Factory put both the Elec and the Manual pumps on with a tee in the supply line, then a pressure Gage on the the fuel rail at the Carb.. I was getting bad readings at the Gauge so I installed a Liquid Pressure Gauge with Regulator at the Carb.. with this setup I have as much pressure as I want ,,, Have seen 10-11 lbs when doing the adjustments ,,, I set the reg at 7-8 and it will maintain 5-6 at wide open ,,, Keep it simple and make sure that U have no restrictions..

RHC

Re: Fuel Pumps Questions.
 

To build on what 42MTI said (Post #8),the 800SC & 900SC use a different pump (p/n 821031) than the 600SC. After following 'more motivation', we're all probably thinking, who cares?

Re: Fuel Pumps Questions.
 

My mech is looking into that with Merc Racing but from my research it looks like the pump for 800&900sc's run off a pushrod mines are off a cam so I wonder if it is compatible.

More motivation...

Re: Fuel Pumps Questions.
 

GLH- Good catch! I really don't know. You're right, my 800SC's have the pushrod. The Merc website doesn't show a pushrod with the 600SC. Let us know what Merc says. This has gotta be right. Funny how we gravitated from 'motivation' to 'pushrods!'

Re: Fuel Pumps Questions.
 

I have seen many fuel pumps that are fine but wrongly accused.
Check the fuel pickup screen for debri, & make sure the rest of the fuel lines are of sufficient diameter and no restrictions. The restricted fuel pickup is almost always the reason for a pressure drop after a long run. Try putting a vacuum gauge at the suction side of the pump, high vacuum & you have restriction that no pump will overcome.

Re: Fuel Pumps Questions.
 

Thanks Jim checking for restriction was done everytime we changed the pumps and the cam.
My mech will again go thru the whole line next week before we head down to FL with the rig.

Re: Fuel Pumps Questions.
 

I checked the pics of the parts at Bam Marine's website.

More motivation...

Re: Fuel Pumps Questions.
 

I will check this when I go up to the boat today I know they are hard lines passed the pump and rubber lines prior to the pump.

This is the merc stock rigging.

I've played with the contrast in order to see but here is how it is plumbed standard from Merc

Click on the pics for the big versions

Pic #1
You see the rooting from the tank to the electrical priming pump at the bottom right from there thru the fuel filter, from there along the center transom over the strainer to the mechnical pumps, the other rubber hose is the return from the mechanical pump.

Pic#2
Stainless hard pipe routing from mech pump up to the fuel rail feeding the two 700cfm Holley's, notice the electrical pressure sensor is at the end of the rail.

This set up is similar between the two engines and one works fine the other is driving me nuts

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Keep the conversation coming....

Re: Fuel Pumps Questions.
 

I use the CV Products billet mechanical pumps on 650 hp motors. I changed the bases with the Mercury sea pump bases. This required drilling the treads out so they would screw together. I tapped the holes as BenPerfected did for the overflow line.

This made for a clean install, but was a little pricey. If you're paying someone to do your work, this would be cheaper than electric pumps with all the plumbing, wiring, safety switches, etc.

The only drawback I have is if I take the fuel bowls off put them back on, I have to fill them manually through the side plugs.