I'm gonna pull my fuel tank down today to remove the sock,been there 30+ years,,,dont' think I need it with two inline filters,,,one before the electric pump,one between the mechanical pump and carburetor. Anyway,been thinking about bypassing the mechanical pump ,,,the only problem I have with this is that my fuel pressure seems to fluctuate when deadheading at the carb with the electric,,,I get different readings from cold to hot,,,do you think it will give me any problems down the road? Will I still get the volumn from the comp140 even though pressure fluctuates 2-3 psi? I wonder if the mechanical is aerating the fuel if the comp is trying to blow thru the carter 120gph pump? Tom,Jason,Ken,anyone? what do you think? I'm using an autogage fuel pressure guage,and it usually reads 10-11 psi cold,8-9 psi hot. It seems to go flat at the top of 1st gear(before 6000),then pulls fine to 6000+ before I shift to third,,,I'd think fuel demands would be higher at the 2-3 shift than the 1-2 shift?? unless all the fuel is at the back of the tank from the launch? I always run it with a half tank of fuel minimum...enough rambling for now, thanks.

Dump the mechanical pump, put a Mallory 4307M return regulator near your carb and use -8 supply and return lines.

I've currently got a Mallory deadhead regulator(that came with the pump) right before the fuel log, I've thought about using the factory return lines off the back of the fuel log. I'm also using the factory 3/8" fuel line. At my power level,its probably enough.

If you're using a recirc regulator you need a return line that is sized for the pump. A 140 gph pump needs a 1/2" return line to keep the fuel pressure under control. The 3/8" supply line would work. My experience with deadhead regulators isn't good, especially if you want consistent fuel pressure.

Robert,

I have had a lot of trouble with the Mallory deadhead type regulators. 3 of them went bad in about 4 years and the pressure was not real constant.

My fuel system consists of a Mallory 140 and matching filter at the tank (sump welded to the stock tank), #10 braided between the tank and filter/pump, and #8 braided from the pump to the regulator. Finally switched to the old reliable Holley Max-pressure regulator. No problems since. Been on about 3 years.

The thing that I noticed with that regulator (the Mallory) is when I would get on the car really hard the pressure would drop quite alot. Pressure at idle was set around 7.5 psi, under full throttle while accelerating, the pressure would drop to about 3-4 psi. Did this with all the Mallory regulators. With the Holley regulator, pressure stays rock solid at 7 psi while accelerating.

I run a copm 140 with the Mallory return style regulator that came with it. Can't remember the number.
I run 1/2" alum fuel line to and from.
Works just fine on an 11.0 car.

I also used to have a situation where the car would lay down above 6000 in low gear, but pull fine to 6500 in 2nd. Turned out it was the transmission. Something was allowing the high gear clutch pack to engage slightly at the top of low gear. The result inside was burned high gear clutches.
I took the trans apart and converted the B&M shift kit to a TransGo -3 and the problem went away.
Just a thought....
Ron

Bob,

I use the mallory return style regulator with my 140 pump. I have mine set at 6.5 psi and the only time I get fluctuations in pressure is when my fuel tank is low. It is at a solid 6 psi at WOT. After a long drive in 90+ heat and the pump is warmer It will go to 6 psi and stay there. I only ran with a dead-headed regulator for a few miles so no experience there.
-10 supply and -8 return. I have 3 filters. one between sump and pump, one between pump and regulator and one at the fuel log.

I want my Carter 172 back !! But I am not touching anything on the car at this point especially the camshaft.

What my current intention is to get the 172 back in working order and leave the 140 off when street driving. When at the track I plan to have the 140 turned on and regulated to 3 or 4 psi to keep fuel up front feeding the 172.

It is strange how much fluctuation in pressure you have from Hot to Cold.

Tom, I've been told its because its deadheaded that I get the fluctuation. The carter pump is supposed to be set at 8 psi and not need a regulator,but it fluctuates also :confused: maybe it has something to do with the sock/pickup? The only way to find out is to drop the tank and see what the sock looks like. I'm also running a lightweight fuel pump rod. What if I hooked up a return line without a return regulator, I'd still have the flow,would the carburetor just take what it needs and let the rest recirculate? Thanks again.

Rob,

The sock would/could cause a fluctuation if the clog in the sock was variable. But I would think the degree of the sock being clogged wouldn't change much. Dropping pressure under hard acceleration could be the sock but I think the fluctuations are from the dead head regulator since this seems to be a common cause.

If you run a return line from say the fuel log after the dead head regulator and Carter, you would lose a lot of volume and pressure right at the carb since the fuel would take the path of least resistence back to the tank. There won't be enough pressure to keep the bowls full.


Unfortunately I have not run a mechainical with an electric pushing (yet). Let me make sure I understand correctly.

Have you run the electric on its own? Have you tried setting it to 7 psi. or has it always been run through the Carter?

Bob, you want to talk on the phone tonight?

I've always run it thru the mechanical pump,never on its own. I pulled the tank down,the sock was black, not sure what color they are originally,and very brittle,so I removed it and bent the pickup slightly more down towards the bottom of the tank and reassembled it. I found the build sheet too,for what its worth. Anyway, I started the car, set the fuel pressure at 8 psi, I was tinkering with the carburetor, went back around and fuel pressure was down to 6 psi after it reached 180-190...I cannot figure out why after it warms up ,I lose 2 psi, without fail. The fuel line runs nowhere near the exhaust,the floats are set right on the money,you can see the fuel at the hole,bump the fender and it comes out,I have blown air thru the fuel lines from up front and it blew fuel out the filler neck. I am stumped. Whats a good time to call Tom? Not sure I'll be home this evening,but might be...Since I'm on vacation and my sis and her son are here,might take off and do something.

Liquid filled gauges give a different reading from cold to hot.

I've seen 3 different working, nearly new gauges on the same car give 3 different pressure readings.

In addition to what Brian said

It could be that the pump is heating up and has a reduced efficiency. Check all the wiring and the pump and relay(s) to see if it is hot to the touch, also check the pump and relay voltage when the first turning it on and when the pump has been on for a while and the pressure drops.

I only lose 1/2 psi after the pump has been running for a while, the bypass regulator reduces the load on the pump significantly.

Bob, I shot you an E-mail with my phone number I call me anytime tonight after 8 pm NY time (gotta get kids to bed)

Bob,

It seems (as with most things) that people all have different experiences to share. Here's my setup:

- factory gas tank and pickup, pickup tube modified from 3/8" to 1/2"
- 8AN from tank to filter
- Mallory filter before pump
- 8AN between filter and pump
- Comp 140 pump
- 8AN to 8AN Russel inline fuel filter
- 8AN from Russel inline filter to regulator
- Mallory 4207 non-return style regulator
- 8AN fuel log to carb

My fuel pressure is 9psi cold and 7.5psi when the engine is at operating temperature. My fuel pressure never fluctuates unless I'm low on fuel. I think how well the regulator performs may have something to do with where it's mounted. I used to have mine mounted directly to the cylinder head. When it was mounted this way I had problems nearly identical to what you're describing. The only thing I can think is that with a hard mount the needle/seat in the regulator was bouncing and causing a variation in the fuel pressure. My regulator is now "suspended" between the fuel line supply and the fuel log. I also ran my fuel line ahead of the regulator to the radiator and looped it back. This way there is a column of fuel that is pushed towards the regulator under acceleration. I also added the -8AN Russel inline filter between the pump and the regulator at this time. I think this may be key as well as it would block any trash that might come from the pump (read not from the tank).

Works mint.

Here is a picture:

http://bellsouthpwp.net/k/_/k_jett/Images/Temp/DSCN2095.JPG

Thanks Tom...Ken, my regulator is mounted similar to yours, except the fuel line loops up over the valve cover towards the fender well,so its mounted fairly rigid. Do you think I'm gettin too much heat from the valve cover, its 3/8's from the tank to the carter, -8an from the mechanical pump to the carb, my fuel log is also similar to yours.

I say the further away from any heat source the better. A few people I know run an insulating wrap around the supply line to further prevent heating the fuel.

We use the Mallory 140 with matching filter and regulator.
No return line.
534' motor with plenty of miles and numerous runs, no problems so far.

No fluctuation in fuel pressure with the deadhead regulator?

Bob,

I use a Comp 140 with a deadheaded Holley big port regulator. No issue with variation.

I was running the factory 5/16" line (307 car) with a Holley blue and the same regulator and started to see fuel starvation problems last year.

My new system was intentionally overkill.

1.)15 gallon aluminum fuel cell with sump.
2.)-10 line from cell to Comp 500 Filter.
3.)-10 line from Filter to Comp 140 pump.
4.)-10 line from pump to Holley big port regulator on RH inner fender
5.) 2 each -6 lines. One to each fuel bowl. (Will probably change to -8 with the new motor)

Originally posted by Rapid Robert:
No fluctuation in fuel pressure with the deadhead regulator? Good question!? but with a best of 10.19 @ 131 mph I don`t think it`s an issue at this point, but who knows.

When we get into our season down here I`ll check to see. It can`t hurt.

Originally posted by kjett:
I say the further away from any heat source the better. A few people I know run an insulating wrap around the supply line to further prevent heating the fuel. Interesting point.

A few smart racers have been known to use an Insulated fuel line cover:

http://www.hobbystage.net/camaro/camaroracer/1091592293-004127.jpg
http://www.hobbystage.net/camaro/camaroracer/1091591550-004126.jpg
http://www.hobbystage.net/camaro/camaroracer/1091591331-004125.jpg
http://www.hobbystage.net/camaro/camaroracer/1091590902-004124.jpg