Another fuel system setup question - fuel / water filter before or after mech pump?
 

I'm switching from an electric to a mechanical pump, and I am wondering if I should run my line from the tank to the fuel/water separator first and then the pump, or go straight to the pump. I believe it went to the filter first when I got the boat and it had a mechanical pump on it. When I went to an electric pump I ran the line straight to the pump because I understood that those pumps are designed to push fuel rather than pull it, but I believe the mechanical pumps are a different beast. Does this make any difference? It would seem to be a good thing to have a filter in place ahead of the pump as long as it can pull the fuel through it without any problems. FWIW, it is one of the Holley 6-valve pumps through 1/2 inch lines.

my vote is filter first.it keeps any trash from entering the valving in the pump.

Merc runs them after the mech pump stock, crazy I know. However, that filter is not much of a filter with a high micron number, it is really more for water.

not...merc sucks fuel through the spin on fuel filter..carb models have a rock filter in the carberator also..(Qjet) i have also seen some efi with and with out in line fuel filters after the feed pump..

Most Merc fuel/water filters are 4 micron, which is pretty fine. I use a 100 micron filter before fuel pump.

with electric pumps: Separator, filter, pump, then another filer right before the carb.

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Bud. I know for a fact that Holley fuel pump will pull at least 762hp worth of fuel through a stock Merc filter head/filter and a 3/8 hose with a little tiny pick-up tube and a whole bunch of NPT 90's all over the place. Not my setup but have been on the boat many times where it went to WOT and stayed there for 15-20 minutes at a time.

Best to pull fuel through the seperator as opposed to trying to push fuel through the filter .

You have been misinformed, the spin on filters from Merc are 10 micron. The inline EFI fuel filters are 4 micron

Well crap, then why am I going through all the trouble to install that larger pickup and 1/2 inch hoses? :picard1: Oh well, going to do it anyway just in case. ;)

I never said it was the right way to do things. Believe me I pissed and moaned about they way it was setup. But at the end of the day it worked. I highly doubt if there was an electric pump on it would have ever worked. The point is those Holley pumps will pull some fuel out of the tank. Last year it was 762hp this year it's 884hp and he thinks the same pickup and fuel lines will do. I did however convince him to stup up to an FST fuel/water separator.

Just bustin' your chops, BB. Thought I'd dole it out some too. :D

with 762 hp and a stock filter head your buddy was playing with a gun with one bullet,with 884 hp that gun is fully loaded.it sounds like your buddy is a lucky gambler.

Boat rolled over 95mph last trip out last year. He and 1 other ejected boat landed upright. No lanyard kept running. Somehow cam back to an idle wheel turn all the way one direction boat spinning in a circle. Late in the day middle of the Bay no boats on the water. One made it back in and shut it down. Yeah, some people can do it all wrong and get away with it. Some can't.

Those rock filters are a good idea in all carbs imo. Was rebuilding a pair of demons for a buddy this week, and found this in his needle/seat.

I saw a two ilmar 700hp plumed wrong and feeding it each through one #4 fuel hose shook my head. Staid that way on one engine I fixed the other.

MERCURY MARINE Water Separating Fuel Filter, 25 Micron, O/B and Mercruiser, Filter

Old style canister filers, were 10 micron for EFI engines, 25 Micron for carb engines.

EFI runs 2 filters?

Yes, most had the spin on filter, plus a filter before the injector rail if I recall right.

Thought so but didn't want to be stupid.... LOL

Heres a 525EFI filter thats pre injector rail. Then it also has a typical style water separator deal too.

Looks like same filter on my engines if you can post part number.

Its on the box in the pic lol

Couldn't read it till I clicked on it. to funny

Hahaa, that is funny chit. I thought you maybe were like Mike Tkach and needed to put on your spectacles to see whats going on here. :D

That sum***** needs to go out and buy a lottery ticket. Yep, some folks seem to live a charmed life like that, while others get zapped in the azz by lightning no matter how careful they are.

Are we supposed to run a filter in front of an electric fuel pump as well? I was running an inline filter in front of mine, and I think this may have contributed to my problem.

Mild, I replied to one of your posts on another thread talking about filter heads for fuel/water separators. You posted a link to Fleet Filters for a filter head, along with a link to a fuel/water separator (PN 33405). I don't have room on my setup for a filter that long, so I'm trying to find a shorter filter that will work with that unit. Found PN 33244, similar specs. Will that one work? Can't remember if it was labeled as a fuel/water separator, but I think the water just settles to the bottom anyway. Let me know if that one will work.

I personally wouldn't run the fuel filter/water seperator before the pump. If you want a filter before the pump then run an additional filter that doesn't filter to as low of a micron level so it doesn't restrict flow as much, but I dont believe this is really necessary with the stock mechanical pump. Filter before the pump is going to restrict flow to the pump, filter after gives some slight pressure downstream of the filter. Better to have a little positive pressure at the pump then to restrict that flow to it.

I agree that the mechanical pump probably doesn't need one, but I thought the electric ones were a lot more sensitive to crud going through them. That's basically what my question was about, in the unlikely scenario where I go back to electric.

Edit: Oops - Now I see that you were replying to my original question, not my more recent one. ;)

So what micron level is really necessary for the big Holley 6-valve pumps and a Holley carburetor? Basically you have a set of rubber fireplace bellows pumping fuel through a garden hose up to a coffee can with holes poked in it sitting on top of the engine, right? :)

Edit: Never mind - looks like that question was answered on page 2. :rolleyes:

Bud I ran the FST Performance setup before the pump which is a 4 micron. The pump pumped fuel like a garden hose. I know this because I was adjusting the valves one time and I had to take of the hose at the fuel rail to get the valve cover off. The stingers in my boat are like a grid system (balsa) it has 12x12 square boxes about 12" deep. Hit the starter button a few times to turn the motor over and I could smell fuel (thinking to myself that's'a strange) so I thought what the heck hold the starter button and see if I can see a leak. Yeah the fuel line was disconnected laying in the stringer box which has a drain hole and a couple revolutions on the motor the box was 1/4 of the way full. At that point I realized how stupid I was but at the same time I couldn't believe how much fuel the pump would move.

OK, this looks like the plan:

1/2 inch line up to the fuel/water filter head, with a WIX 33244 filter on it - that one has a 19 micron rating and flows 12-15 GPM. 1/2 inch line from there to the Holley 6-valve pump. Probably #8 AN line up to the fuel pressure gauge, splitting off to #6 up to the carb.

Do I need some kind of filter before the fuel pressure gauge? If so, is there something that will just screw in-line at that point?

The tolerances depend on the pump, like a holley is probably not that bad and you could be ok, but something like an a1000 has tight tolerances. On an a1000 install Aeromotive says a pre filter is necessary, and wants it to be 100 micron. Obviously this is pump specific but physics are physics. If you put no filter before the pump there will be less restriction then if you put a 100 micron filter, and a 100 micron filter before the pump will have less restriction then a 20 micron filter, so on and so forth. So the question is do you want to restrict the flow to the pump? My answer is no, I want to supply my pump with as much fuel as it wants, I use what I need, and return the rest to the tank.

Something else to consider. Micron ratings do not depict flow. You can have a 10 micron filter that flows more fuel, or say less restriction, than another brand/style 100 micron filter.

I dont have engineering numbers for you Budman, but all I can tell you, is I've been running 800HP blown with twin 850's, with a -10 line from tank to 33405 filter , then to the inlet of a six valve holley pump with a -10,, and #8 up to the carbs where it splits into 3/8 hard lines. I have friends with same setup that has supported over 900hp blown.

I think you'll be just fine with that setup on your 575hp N/A single carb engine.

Thanks MT! I have an existing #6 line that went from the pump outlet up to the fuel pressure gauge / split. Was planning to step up a size here, but now wondering if that Holley pump would be able to push enough fuel through the #8 line. What do you think?

Also, should I stick an extra filter in after the pump?

I appreciate all the help!

As stated in last post, I have -8 line from pump outlet, feeding twin 850 carbs on the blower. The pump is fully capable.

I would strongly consider the filters at the carb fuel bowls, like these. Everybody likes throwing them in the trash because they think they are a restriction. As long as they are changed on a regular basis, they will move more flow than the .110 needle can.

http://allcarbs.com/detail.php?pid=7...&ctgn=61&stt=0

Budman, those little filter thingy's I am talking about....you may find local under any of these part #s, from oreillys, advance, autozone, napa, etc.

AC Delco GF455

Holley 162-500

Fram CG13

Wix 33050

Purolator F10021

Do those slip in behind the fitting in the carb inlet? Do they require a spring to hold them against the fitting like the Qjet ones do?

Thanks!


Edit: Never mind Mild, answered my own question!

http://www.summitracing.com/parts/hl...FQEcaQodix0A4Q

Hmmm, the Summit listing says that these things also fit Q-jet inlets. Logic would have it that it would go the other way as well. I have a bunch of the little screen filters from various Q-jet rebuilds. I might see if one of these would work. I would think that they would flow about as well as the metal filters.