Thread: Where does my second fuel filter go???

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Hello Everyone! .... I have a Mallory canister style fuel filter that is mounted behind & below my fuel cell & behind & below this I have a Holley Blue fuel pump. I ran -8 an fuel line to the front of my car {a '32Ford}. Now I am planning on mounting my fuel regulator on the firewall & running -6 an line to my carbs {dual double pumpers, feeding a blown 392}. My question is; is it ok if I run my second fuel filter {I was going to get a Earl's} into my regulator or would it be better to plumb them closer to the carb's? Thanks Bill

Rule of thumb - your main filter goes BEFORE an electric fuel pump and any secondary filter - wherever it fits best but generally near the carb.

....Thank You IC2, yes my 1st. filter {the Mallory} is right out of Fuel Cell. I attached a pic of my carb set-up. I could either put a filter right into the fuel pressure regulator or right into the fittings that you see in the pic's. Going into the reguator would be cheaper/easier so I'll do that! Thanks again, Bill

Don't forget to put a shut off valve between the fuel cell and the first filter!!!!!

So if your running a mechanical pump should the main filter go before the pump too?

Originally Posted by stovens

So if your running a mechanical pump should the main filter go before the pump too?

While you can (should??) put a non restrictve filter before the mechanical pump, there should always be one between it and the carb.

With an electric pump you are first trying to protect that tight clearanced rotor then secondarily the carb. The mechanical pump valves can tolerate some level of dirt so here your primary objective is to protect the carb (does that make sense)

Well my wiring work is much lower quality than other work on this Forum and I will try to clean it up, but about a month ago I did finish my fuel system installation. I was able to use a left over piece of stainless steel sheet to bolt to two fender bolts to provide a mount point to the replaceable filter I got from Speedway. I got a shut off valve from JEGs and put that before the filter so I will be able to change the filter with the valve closed. I am not as ashamed of this as for my wiring so far and it seemed to turn out pretty well with a long 3/8" steel line under the right (passenger) running board up to the mechanical pump on the SBC 350. I am a little worried that due to my large rear tires and rear spring setting to clear the tires the rumble-seat-tank is actually about 1" higher than the carb base at the engine which might lead to a siphon through the carb. That condition only holds when the tank is topped off completely full but might be worse when parked on a hill. I bought an electrical shut of valve but I have not installed it for simplicity hoping the float needles in the carb will seal the fuel when the engine is not running, BUT if I do experience siphoning I can install the electrical shutoff valve in the line from the mechanical fuel pump up to the carb. Maybe as I gain more skill with the wiring I will add that valve anyway. Actually the tubing looks pretty good here but each piece is at least the third try! You can see the vent hose because I have not yet drilled a hole through the quarter panel to the fender well for the vent. I have tested the space under the filter bowl and it can be removed and replaced with mount shown.

Don Shillady
Retired SCientist/teen rodder

Originally Posted by IC2

While you can (should??) put a non restrictve filter before the mechanical pump, there should always be one between it and the carb.

With an electric pump you are first trying to protect that tight clearanced rotor then secondarily the carb. The mechanical pump valves can tolerate some level of dirt so here your primary objective is to protect the carb (does that make sense)

Yes thanks!

So it looks like I need another filter between the mechanical pump and the carb. It is going to be interesting to prime that system so I don't have to crank the engine a lot on the first start. Maybe a suction bulb wil pull gas through all of that restriction. On a previous car (MG midget) I had a whole box full of plastic see-through filters with small paper filters inside and they flowed pretty good. They were just inserted in the fuel line before the carb and held with clips; I changed them frequently due to a rusty gas tank but I could see if anything was in there. With my first filter shown above I would think the gas should be pretty clean after the first few minutes flushing the new line. Now I have to rethink another filter.

Don Shillady
Retired Scientist/teen rodder

I have a Fram the same size as Don's located just ahead of the fuel cell. The question I have is, why does every one have so many filters? One would think the large canster filter would be "overkill" as years past saw only a glass sediment bowl, and I am sure there was more trash in the old tanks.

Originally Posted by John Brian

I have a Fram the same size as Don's located just ahead of the fuel cell. The question I have is, why does every one have so many filters? One would think the large canster filter would be "overkill" as years past saw only a glass sediment bowl, and I am sure there was more trash in the old tanks.

I use two filters because of all the junk in fuel these days.... I don't know if it's because of additives at the refinery, careless fuel transfer, or poorly maintained tanks but there is a lot of contaminents in the fuel.... If it sits in the tank for any amount of time, things get even worse..... It doesn't take much to upset the performance of an engine..... The cars with the sediment bowls usually ran an old Rochester or Carter carb, the Holley's and Edelbrocks that a lot of people use now are way more intricate and have more systems withing the carb, thus being more sensitive to contaminents.

For me, the extra filtration is somewhat comparable to an insurance policy, maybe not all the fuel I buy is junk, but if the extra filter prevents messing up the carb one time (usually happens during the final round or many miles from home) it pays for itself......

Besides it looks cool!

Both Dave S and Stovens have the right answer.

I originally built my car to run with an electric fuel pump and had the primary filter mounted on the frame just before the pump and a little one in the line before the carb. I converted to a mechanical pump (not really ea$y on a $B Ford - if it has the wrong timing cover). I did away with the canister filter and am now using a 40micron Speedway race car type unit.

This one