Polishing filter upstream of mechanical fuel pump?

[scratchee]

I've just reinstalled my mechanical fuel pump and carb after a rebuild. I have the polishing filter kit from Moyer (a new addition to my fuel system), and in looking at the installation location, I'm wondering if it would really be a problem to put that filter right next to my primary filter a few feet away. I know that ideally I'd want it immediately before the carb, but if I put it next to the other filter the only thing I'm adding to the post-filter path is a few feet of hose and the mechanical fuel pump. And I'm thinking that if the mechanical fuel pump is putting debris into the fuel line then I'm probably not going to be running much longer anyway. The advantage, on the other hand, would be fewer fuel connections (and a shorter and more direct path) in a less accessible area right next to the engine. Has anyone done something like this?

[Al Schober]

Another consideration.. I had a polish filter right before the carb that was sending its own corrosion products to the carb! Filter was of steel construction, and corroded internally due to moisture in the fuel. I lost a lot of sailing time one summer tracking that one down.
If you install one, check it with a magnet. I think an aluminum one is good to have - catch the corrosion products from the main filter. DO NOT use a plastic one - fire hazard.

[Surcouf]

back to my design engineering days... it is "harder" for a pumping system to have pressure loss at the suction that at the discharge. I think it is called friction loss.
Moreover the more pressure loss at the suction, the higher the chance to get air ingress, as you increase your negative pressure at the pump suction.

but this is just engineering... reality is different, and I go by a simple rule: I do whatever Don Moyer recommends!

[scratchee]

...the more pressure loss at the suction, the higher the chance to get air ingress...

Interesting, thanks! I'll have to take a look at the pressure drop across that filter.

I go by a simple rule: I do whatever Don Moyer recommends!

Yeah, I may end up just doing the standard installation right at the carb. It's certainly doable. I just like the idea of better access to the filter and connections out by the other filter.

[joe_db]

Pressure side filters like putting a RACOR after the fuel pump are not legal for boats or at least won't pass ABYC. Besides for that, if you get a load of crap in your fuel do you want to be changing elements or fuel pumps?
The Moyer filter is "sort of" OK because it doesn't come apart or unscrew. Speaking of, mine has been on for ages and ages. I need a new filter, not a whole new kit. Where is the listing for just the filter??

[scratchee]

Pressure side filters like putting a RACOR after the fuel pump are not legal for boats or at least won't pass ABYC.

I'm not sure I understand what you're telling me. I have a bronze Perko before the fuel pump, and I bought a polishing filter that's recommended to put after the pump. But I'm considering putting the polishing filter before the pump for ease of access.

[ndutton]

What do you think the inline filter will do for you? The answer to that may determine where in the fuel path it belongs. MMI lists their inline filter as 7-10 micron, MMI's Racor filter is 10 micron, if using something other than the Racor, most of them are 10 micron too (the Sierra 18-7945 for example).

[scratchee]

What do you think the inline filter will do for you?

Good point. I guess I want to make sure I get everything the primary filter missed, mostly to maximize engine reliability. The primary is an old Perko and the element looks like a sea sponge (slight exaggeration) so I can't imagine it's better than 20-30 microns.

[ndutton]

Okay, it sounds to me like the primary filter needs a lot more attention (replacement/upgrade?) than placement of the polishing filter.

Consider this:
If you place the polishing filter where you're suggesting you'll have no filtration after the filters, through the pump and all the way to the carb. With the polishing filter in the MMI position it is the last line of defense before the carb. I'm thinking you might be giving up the intended benefit of the polisher.

[scratchee]

Okay, it sounds to me like the primary filter needs a lot more attention (replacement/upgrade?) than placement of the polishing filter.

Consider this:
If you place the polishing filter where you're suggesting you'll have no filtration after the filters, through the pump and all the way to the carb. With the polishing filter in the MMI position it is the last line of defense before the carb. I'm thinking you might be giving up the intended benefit of the polisher.

This is all part of a general fuel system overhaul because my A4 got harder and harder to start at the end of the season (I've been through numerous other threads on that topic so that's not my intention here). Anyway, I rebuilt my fuel pump and carb as part of a potential fix, and figured I'd go ahead and address the filters while I'm at it. I intend to replace the Perko with a newer Racor or similar at some point, but probably not now just for budgetary reasons.

By the way, while working on the carb I discovered a) a bunch of the chalky stuff that I assume is related to ethanol, and b) the two halves didn't mate well, so I machined them for a better fit.

In the next few days I should have everything back together and I'm sure it'll fire right up!

[ndutton]

By the way, while working on the carb I discovered a) a bunch of the chalky stuff that I assume is related to ethanol, and b) the two halves didn't mate well, so I machined them for a better fit.

That's not my experience with ethanol blended fuel at all. I have run a steady diet of E10 for 15 years with no chalky white residue. I suspect you have ingested water in the system that made it to the carburetor and remained there for some time. What you have described could explain your hard start problems. Whenever the budget allows, a higher grade, better condition water separating main filter may solve everything.

Any reaction to the discussion about the position of the polishing filter? That is really what you asked about before I deflected to the main filter (and continue to do so).

edit:
If there is water in the system, where did it come from? That is the real problem, not how to manage it.

[scratchee]

If there is water in the system, where did it come from? That is the real problem, not how to manage it.

I'm thinking along the same lines. The Perko does have a water separator, and I didn't see any standing water in it when I drained it for this project. But I have read that E10 absorbs water, even from humid air (I'm in very humid Maryland), and I thought this could be the source of the chalky buildup which in turn could have clogged passages in the carb. So I'm hoping a fuel system overhaul, potentially including a new tank (I have to measure to see if it requires cutting up the cockpit!), might at least remove the fuel as a source of uncertainty.

I really appreciate the help by the way!

[ndutton]

Did you find this thread from three years ago?

http://www.moyermarineforum.com/forums/showthread.php?p=103779

[scratchee]

Did you find this thread from three years ago?
http://www.moyermarineforum.com/foru...d.php?p=103779

Actually, I hadn't seen that. Thanks a bunch! Very informative.

My filler cap is on the cockpit sole, and it has gotten flooded with rain a couple times when the drains clogged. I've never seen any water in the separator but it's quite possible that water did get into the tank.

[ndutton]

The purpose of the math exercise in that old thread was to calculate for ourselves the real world insignificance of assumed water contribution to the fuel stored in a vented tank of typical volume due to atmospheric humidity. Without the word salad, it's less than ½ teaspoon in a 20 gallon tank, worst case. You probably get more than that from the swill pumped in at the fuel dock.

My filler cap is on the cockpit sole, and it has gotten flooded with rain a couple times when the drains clogged. I've never seen any water in the separator but it's quite possible that water did get into the tank.

This sounds like a much more logical source of water (how often do you replace the fill plate O-ring?) in the fuel. There's another thread about that. The O-ring is mentioned in post #1, water separating filter discussion starts at post #7.

http://www.moyermarineforum.com/forums/showthread.php?t=11084