Carb fuel filters

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70Duster340

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When I had the 340 built, the fellow who did the build suggested that the sintered brass filters be removed from the fuel bowl inlets, and an inline fuel filter be added between the tank and the fuel pump. Before I jump back into this, what's y'alls opinion?

Thanks
 
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I never liked those and I don't know why. We used to replace them with the small pleated replacement filters. A metal can filter between the pump and carb is a better idea. THe pumps don't have much suction and a filter between the tank and pump isn't a good idea.
 
I have always hated those brass filters. They have very little surface area and clog easily. I remember beating on a carburetor with a wrench in my youth to dislodge dirt in one so I could make it home.

I usually remove them, but if you put an inline fuel filter between the pump and the carb they will never clog up anyway.
 
I'm for a filter between the pump and carb as well.
FWIW, I checked the Holley fuel filters on their site. Looks like they don't even give a micron rating for them when you narrow down the results or look in the "specs".........
upload_2020-4-12_8-36-25.png

Filters - Holley Performance Products
 
70Duster340 said:
When I had the 340 built, the fellow who did the build suggested that the sintered brass filters be removed from the fuel bowl inlets, and an inline fuel filter be added between the tank and the fuel pump. Before I jump back into this, what's y'alls opinion?

Thanks
Click to expand...

I run a Holley canister filter before the electric pump (like the directions for the pump said) and the inlet brass filters both.
So far no problems with either.
I have seen some recommend removing the ones in the inlets, but if they are not causing problems I can't see removing them.
Not running a filter before the pump is asking for a pump failure and a voided warranty.
 
I don't have an electric fuel pump, just the mechanical type. It's a Carter OEM type. Does the make a difference?
 
70Duster340 said:
I don't have an electric fuel pump, just the mechanical type. It's a Carter OEM type. Does the make a difference?
Click to expand...

I suppose it could, but I seriously doubt it.
The big difference between the two is the electric pushes fuel and the mechanical pulls it.
AND most any fuel pump manufacturer requires a filter before either type.

The main thing I think is to just keep an eye on the ones in the inlets so they don't get plugged up.
But then again, if they did plug up then without those filters all that crap would go right into the carb.
 
I see what you're saying, but I am a bit nervous about cutting the metal fuel line to put in the filter. Any other place to put it?
 
The EFI practice is to run a 100 micron filter before the electric pump and a 10 micron after it to the injectors. They deal with much smaller crap than a carb or check valves in a mechanical pump. Mechanical pumps would be fine with a 100 micron pre pump filter and a 40 micron carb filter. EFI pumps offer low vacuum and they can pull through a 100 micron easily so the high vacuum of a mechanical should pull right through no problem as it already pulls from ~10 feet away in dinky 5/16 line as it is. The sintered bronze rating was 40 for a GM QJ. Their trouble (?) was the small surface area of the filter element, not the material.
 
Back in the day, Just about every car on the road with a mechanical fuel pump had one between the fuel pump and the carburetor. I am counting the brass one in the carb inlet in this category.

The easy way to do this is to put it in the hose that connects the fuel line on the frame to the engine.
 
IIRC the standard sock on the sender was ~300 micron but many have long dissolved and you would not even know it unless you pull the sender.
 
70Duster340 said:
I see what you're saying, but I am a bit nervous about cutting the metal fuel line to put in the filter. Any other place to put it?
Click to expand...

I have run them right where the sender transitions to the steel line at the tank.
Generally there is a small section of rubber hose there already.

Mike69cuda said:
Back in the day, Just about every car on the road with a mechanical fuel pump had one between the fuel pump and the carburetor. I am counting the brass one in the carb inlet in this category.

The easy way to do this is to put it in the hose that connects the fuel line on the frame to the engine.
Click to expand...

A quick story, (I know, like everybody has one):D
I watched 4 guys screw with this car for days, starting it and driving down the street only to come back pushing it.
Long story short, I went to my tool box and grabbed one of those Q jet paper filters and went over and handed it one one of them.
They didn't speaka da English and the guy looked at the filter and back at me with a questioning look, so I pointed at the carb inlet (big one inch fitting) and went back home.
Next thing you know they were driving it around, and even back home.:D
I don't know what they were saying but they kept pointing a my house and slapping their foreheads and laughing.
 
70Duster340 said:
...I just want to protect it as much as possible.
Click to expand...
Lol, "a belt and suspenders" eh, can't blame ya'.:D (kiddin)

IMO, if you're bent on a pre-filter besides the pickup, 100 mic max prior to the pump, and a 40 mic as close to the carb you can get. The way I see it, the closer to the carb the less contaminate possible after the filter.
 
I have run a pre-filter on a stock fuel line system with a Carter mechanical pump. But after changing out my fuel tank and installing new fuel lines I know that contaminants are minimal. I now just run a good quality filter after the pump.
 
Definitely not set on the pre pump filter, just was asking the experts, since the pre filter was recommended by the engine builder. Everything in the fuel system is new, including the pump.

Would a filter with a replaceable element be sufficient?
 
TrailBeast said:
I suppose it could, but I seriously doubt it.
The big difference between the two is the electric pushes fuel and the mechanical pulls it.
AND most any fuel pump manufacturer requires a filter before either type.
Click to expand...

The mechanical diaphram type pumps have poor suction characteristics. Never place additional restrictions on the suction side if can be helped.

One filter on the tank pickup. That's the 'sock' which should be formed such that it holds its shape even under light suction. If it collapses it will kill flow. Seen it happen even with a breass screen in gravity fed sno-throw so you never know.

One in-line filter between the pump and the carb inlet(s). This should be a finer filter. Any decent replacement filter will work. Most use a paper media. If using a screen type then micron ratings and flow rates can be looked into. Otherwise don't worry about it.

The outlet of the filter must be higher than the inlet.
Chrysler Master Tech Sevice Conf. 1963, Carburetion & Performance page 13

The sintered metal filters won't hurt. Most are spring loaded allowing them to be bypassed if clogged or in the way of demand.
That said, I like just about everyone else who planned on going to the drag strip removed them.
Truth is, there's enough fuel in the bowls to just about carry a car to the 1/4 mile mark even with poor refill. Talking a 14 second car or slower. You can guess how I know this...
 
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I think the mechanicals can pull more than most think. You can boost reference a mechanical fuel pump to upwards of 9 psi plus the 4-5 they put out. IIRC the lever motion of the arm against the eccentric retracts the diaphragm (suction) and the spring pushes it back to give it its constant pressure. If you pressurize the free side (via sealed weep hole) with boost, you are increasing the 'spring' pressure thus increasing the fuel pressure over the stock rating.
 
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