Marine Fuel Pumps

[Craig]

Can someone tell me if, in general, marine fuel pumps are higher volume / higher pressure pumps than stock automotive ones. I repowered last year, and since my boat never sees salt water and is usually on a trailer, I cut a $$ corner and bought a standard automotive fuel pump. The main problem is I'm not getting the recommended WOT rpms with the new engine and I don't think its prop related. I noticed an additional decrease in rpms after installing a large in-line fuel filter and that got me to thinking that maybe I have been experiencing some top end fuel starvation, the addition of the filter just adding to this problem. I am planning on doing a couple of checks suggested in my Volvo shop manual for fuel pump volume and pressure, but just thought I'd post this question regarding marine pump volume vs automotive pump volume to see if maybe I should just change that thing. Still have my old pump which actually is probably still functional. Might just try it to see if there's a noticeable difference. Appreciate any help!

[BillG]

Dangerous move. The volume and pressure should be the same but the safety sure isn't.
Marine pumps have a port to attach a hose that is used to allow fuel to be bled into the carb in case of pump diaphram failure.

[RickR,GroveCity]

Craig
I agree with Bill
Also, go to your local discount auto parts any buy a fuel pressure tester for a fuel injected gas engine.
Check your pressure on the carb side of the fuel filter. For BBC about 6 or 7psi@WOT
Save your pressure tester for your fuel injected auto.

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RickR mailto:riggerb@aol.comriggerb@aol.com</A>

[AVickers]

I don't know that an automotive pump would cause fuel starvation at extend WOT, but I know that marine equipment is set up for that kind of running and auto stuff typically isn't. Extended full throttle running in a car or truck is very unusual...

For instance, one thing I've noticed, at least with the Q-Jet carb, is that the needle $ seat on the marine application has a larger opening -- significantly larger -- than its automotive counterpart. It's also stainless steel rather than brass.

As for safety, I agree that marine gear should be used... I think that by law, any leaking fuel has to be vented into the engine: either to the intake of the carb, or, as a second choice, into the crankcase. Almost all marine fuel pumps have a second hose running from the top of the diaphram chamber that vents back to the tank or to the intake side of the pump (or, in some cases, to the carb intake).

Carter automotive pumps have an opening on them into which you can install the nipple from your old pump (if it's a Carter) and they cost about $40 less than the marine version... The other option would be to run a fully sealed unit where, if the diaphram leaks, it leaks into the crankcase. You have to watch your oil carefully if you use this setup 'cause if you lose a diaphram, you get gas in the oil which, if run, would ruin the bearings and cam... Having run Triumph cars (and having used Holley carburators) for years (both of which can leak fuel into the crancase), I'm just in the habit of sniffing the dipstick anyway, but not many people are in the habit of doing this...

Has anybody out there run a Holley electric pump w/ an oil pressure shutoff? I don't see how one of these could leak, but don't know if they are marine certified. This setup would cost slightly less than a mechanical marine fuel pump setup, but might have some advantages in terms of precharging the float bowls before you begin cranking the engine to do the same -- a definite battery-saver after the boat has been sitting a while...

[Hornetman]

OK Guys, Here's the scoop with my fuel pump situation. I need one and I haven't been able to locate a marine pump for a 427 (ford). Any suggestions? Would the Carter pump for Ford FE also have the hole referenced by Mr. Vickers? Would I be able to modify a non marine pump to make it safe(er)? Thanks


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Steve A. (Hornetman)

[Craig]

Thanks for the info. guys. I went to the expense of a new marine carb, I guess I might as well get the marine fuel pump. I'd rather not blow up the boat. I am still curious if the marine ones are made any different, as avickers said, to better achieve adequate fuel flow at extended full throttle running. Might just reinstall the old marine Carter, for now, to compare. As I said, I don't think anything is wrong with it other than it was old. Probably o.k. to use. Thanks again!

[Forrest]

Also, marine fuel pumps have dual diaphragms. The only time fuel will be present in the clear hose that goes from the fuel pump to the flame arrestor is when the main pump diaphragm fails. The second diaphragm is to keep fuel from entering the crankcase if the main diaphragm fails. Even if the main diaphragm fails, the engine will keep running because the second diaphragm is now moving the gasoline, though a dangerous condition exists. The connection for the clear hose on the fuel pump is to the area between the two diaphragms and is there solely to monitor the condition of the main diaphragm.

Always use a marine-grade fuel pump on a boat. Summit Racing Equipment (http://www.summitracing.com/) has a good price on Holley marine fuel pumps (http://www.holley.com/HiOctn/ProdLine/Products/Marine/FMS/FMSFP/712-327.html).

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Forrest

[This message has been edited by Forrest (edited 05-22-2000).]

[AVickers]

No doubt about it! I'd go for the Holley.

The Unit Forrest mentions is $80 at Summit. The Marine Carter I looked at was $115 at BoatUS. The Carter Automotive was $70 at NAPA.

BTW. I have had the Carter apart, but didn't find two diaphrams. There was a regular diaphram and above it was a rubber plug up in the housing body around the actuator rod, that might function as a diaphram, but it appears that the rod simply moves up and down in the center hole of the plug. The plug appears to act as a barrier between the top side of the diaphram housing and the crankcase. On my boat, the hose to the nipple that vents this region is not clear and it connected not to the flame arrester, but to the tank side of the spin-on fuel filter.

At some time did the Coast Gaurd mandate that the hose be clear and attached to the top of the carb (or flame arrestor) on more modern boats? Unlike my SB 18', my BB 22' is set up just like you describe...clear hose to the top of the carburetor.

Also -- The guts of the Carter marine and automorive carbs were identical -- the castings, valves and screnes, and hole sizes were all identical. The automotive pump body was even drilled to vent the unit at the same spot the marine unit has a mipple -- only difference I could find was that there was no nipple installed. On the car unit, my guess is that if the diaphram goes out, it leaks onto the ground under the car...

[This message has been edited by avickers (edited 05-22-2000).]

[Forrest]

Back in the '70s instead of using a clear tube to the flame arrestor, often times on the side of the fuel pump you would find what looked like a glass-bowl type fuel-filter off of some early 1960's car. The only difference was that the was no filter in the bowl, but there was a little sign that read something like, "Replace fuel pump if gas appears in bowl."

Sometime back in the mid to late 1970's, the USCG changed the rules declaring that glass bowls that do or can contain fuel were not safe and would not meet approval in new installations. That is when you started to see the clear tubes, carburetors with J tubes, and no more Racor filters with clear sediment traps.

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Forrest

[Rich]

Marine fuel pumps many times have a catch can on the bottom to prevent fuel from leaking out the vent hole in case the diaphram leaks.

[Craig]

Checked via some part numbers re: my old Carter fuel pump and turns out it wasn't a marine pump either, so I guess, basically my boats been "dangerous" for 30 yrs!!! I'm going to check on the Holley and with Summit. Thanks guys! I am, now, mostly replacing it for safety purposes, but the psi for the marine pump, which I also got a Carter number for, was a bit higher than the old one and the cross referenced newer automotive one (6.8psi vs 5psi). My Volvo manual says for V8 engines pump pressure should be in 6psi to 8 psi range, so maybe theres something significant in that difference with regard to top end fuel starvation and my engine not reaching its specified WOT rpms. The Volvo maunual does state that too low pressure from fuel pump will cause this. Well, gotta go change a pump. Thanks again for all the advice.

[BillG]

You could have a fuel starvation problem if you have a fuel filter other than a screen type between the tank and the pump. The pump will push the fuel through a filter easier than pull it through.