Two fuel filters? One at tank, one before carb (72 GMC 1500)

[centuryhouse]

Yesterday I realized that my 72 GMC (350 w Holley carb) has a see through plastic fuel filter at the tank behind the seat on the passenger side (before the pump), and has another in the fuel line between the pump and the carb.

Is this typical? Will two filters create extra restriction on fuel flow?

I've had a problem that is yet to be resolved, where if I punch the gas the engine will immediately drop rpm for a second or so, occasionally even die. The timing seems fine, the carb could use a rebuild I bet, but seems to jet fuel just fine. Could having two filters cause this?

[Alex V.]

My Suburban has two (one about halfway back on frame, other right beside the air cleaner) and it's never caused a problem. I don't think a conventional size plastic/paper filter would cause anywhere near enough restriction to cause any problems even in tandem, as long as it's clean.

[centuryhouse]

Another question: is there any reason I should run more than the one behind the seat (before the pump)?

Yesterday I noticed a gas smell about 5 minutes after I started the truck, and realized there was gas running all over the engine, and pooling up under the truck. The recently replaced filter on the engine (after the pump) was leaking everywhere.

I'd like to do away with the filter on the engine, and just run with one filter before the pump, to lessen the fire hazard.

[dfrank]

Originally Posted by centuryhouse

Another question: is there any reason I should run more than the one behind the seat (before the pump)?

Yesterday I noticed a gas smell about 5 minutes after I started the truck, and realized there was gas running all over the engine, and pooling up under the truck. The recently replaced filter on the engine (after the pump) was leaking everywhere.

I'd like to do away with the filter on the engine, and just run with one filter before the pump, to lessen the fire hazard.

I don't think the fuel filters are your problem. It sounds like you have a stuck needle in one of your float bowls. That would explain the gas running all over the engine and pooling up on the ground. It would also explain the stuttering and the engine stalling from being flodded with fuel. I would rebuild that carb if I was you. Good luck!

Edit: Just reread your post and saw you said the fuel filter was leaking. Try replacing that filter and checking all your lines. A second fuel filter can't hurt anything.

[centuryhouse]

Would NOT having the post-pump filter hurt anything?

[AirSpeed]

I would keep the post fuel pump filter, debris coming off the fuel pump diaphragm could enter your carb, plug your float valve. I have two filters on my truck, a large steel one under the cab below the fuel tank and one in the carb, even with two filters I've have found debris in the carb filter.

[waco]

I have dual tanks on my 76 k20. 1 filter for each tank before the swiitching valve. 1 filter after the switching valve & before the electric fuel pump. And 1 more filter between the pump & my Holley Pro Jection throttle body. That setup gets me 10 lbs of pressure on the supply (3/8" line) & 4 lbs pressure on the return line (1/4" line). Never had a single problem. As long as you service filters on a regular basis they never be a cause of restriction. IMO

Andy

[GASoline71]

To the OP... Get rid of the fuel filter behind the seat. Especially a cheap plastic one. It's a fuel leak waiting to happen. These rigs came from the factory with a fuel filter in the carb inlet. So a filter between the pump and carb is all you need.

Originally Posted by waco

I have dual tanks on my 76 k20. 1 filter for each tank before the swiitching valve. 1 filter after the switching valve & before the electric fuel pump. And 1 more filter between the pump & my Holley Pro Jection throttle body. That setup gets me 10 lbs of pressure on the supply (3/8" line) & 4 lbs pressure on the return line (1/4" line). Never had a single problem. As long as you service filters on a regular basis they never be a cause of restriction. IMO

Andy

7 filters if I read that correctly... that's overkill...

Gary

[100%Chevy]

I'd advise everyone to get rid of the glass and plastic fuel filters!
Here is a video I made of the plastic one on my 82,C-30.It is temporary! The truck never left the yard like this.Watch the inlet hose flexing in and out.Won't be long there will be a gas leak!


The video may not work for everyone.

Mike./

[centuryhouse]

Originally Posted by 100%Chevy

The video may not work for everyone.

Mike./

It worked. The plastic one behind the seat looked like that one, and the inlet side had weakened and instead of being hard plastic, was weak and almost rubbery, moving like that when I moved the filter by hand.

The filter between the pump and before the carb was new, $20, glass and metal, and leaked everywhere. Turns out you can unscrew it open to change the filter element. When I bought it I didn't realize that and just installed it. I should have twisted it to tighten the ends so it wouldn't leak. My fault for not knowing, and their fault for having no instructions.

I've used a metal filter once, but quit using them when I tightened it and the metal end ripped off.

I don't really trust any of them at this point, but I'd guess metal is the best :-/

[dfrank]

Originally Posted by centuryhouse

It worked. The plastic one behind the seat looked like that one, and the inlet side had weakened and instead of being hard plastic, was weak and almost rubbery, moving like that when I moved the filter by hand.

The filter between the pump and before the carb was new, $20, glass and metal, and leaked everywhere. Turns out you can unscrew it open to change the filter element. When I bought it I didn't realize that and just installed it. I should have twisted it to tighten the ends so it wouldn't leak. My fault for not knowing, and their fault for having no instructions.

I've used a metal filter once, but quit using them when I tightened it and the metal end ripped off.

I don't really trust any of them at this point, but I'd guess metal is the best :-/

You could always switch to AN lines and fittings. I have never had a fuel leak with them.

[centuryhouse]

Originally Posted by dfrank

You could always switch to AN lines and fittings. I have never had a fuel leak with them.

What is AN?

[waco]

GASoline71

Only a total of 4. 1out of each fuel tank to catch junk that might come out of the fuel tanks before the tank selector valve (2 standard 3/8" metal type filters). One 100 micron filter after the tank selector valve but before the fuel pump. And 1 just before the new lines I bent for the throttle body to catch any thing that might be the OE line after the pump. I reused the OE fuel where I could & this just made since to me to protect my $600.00 investment. It just my way.

Andy

[RonG]

Originally Posted by centuryhouse

What is AN?

AN is Army/Navy...military specs...37 degree angle seat for fittings used with braided steel lines. Google it for more info.