[72projectbird]

So I picked up a 77 TA from GA. When it arrived the fuel pump was dead. Would run fine with the fuel bowl filled up, but the pump wasn't pulling any fuel. I hooked an electric Carter pump up just to get the car moving, and it worked great.

I just installed a new mechanical pump (Carter M6122) which looks just the same as original, with the larger canister, and return line output.

As soon as I installed it, the engine flooded immediately. I checked for a stuck needle, or sunken float, but everything is fine. When I went to crack the fuel inlet line on the carb, it was extremely pressurized. So I crawled under the car to see if the return was plugged, and when I removed the return from the pump it shot fuel out with enough force to cover the front disc brake.

I compared the old pump to the new, and the only difference I can see is that the return port on the new pump is the size of a pinhole compared to the original. I opened up the opening with the correct size drill bit, but it still is creating a ton of pressure at the carb inlet.

Is there something stupid I'm missing?

[locomotivebreath]

I think it’s a crap shoot with the quality control on mechanical pumps these days . About 10 years ago , I went through 3 pumps to find one that had the correct psi . A Delco and 2 airtex . One of the airtex pumps worked . This was on an unmodified goodwrench 350 chev with an edelbrock Qjet . One pump was 10psi . I also suspect that these pumps are all the same manufacture but different boxes .- I can’t confirm that though . My GTO has a new Delco unit that’s atleast 15 years old but I haven’t ran it yet to report on .

[Formulajones]

I'd probably take the pump back and have them swap for another to try.

About 3 years ago I had a fiasco with mechanical pumps and went through 3 of them in 2 days. Just a simple air cooled VW bug pump, nothing fancy. Made by the same companies that make the V8 stuff and all sold at the same chain stores.
First one didn't get out of the neighborhood and just died. 2nd one got about 10 miles from the house and died. 3rd one was a charm and has been on there for about 3 years now and still working fine.

Haven't had to buy one for anything since but I'd imagine not much has changed.

They are a crap shoot anymore.

[77 TRASHCAN]

Hmm seems like mine did not have the larger cannister???

Your ordeal is a common situation these days. Especially with mechanical fuel pumps. I have sold them all, although not since 1998.
Back then all the brands were identifiable by brand, I guess not much any more.

I've thought about buying one of those RobbMc pumps, for even just a stockist build. I know their stuff is legit.

[taktikian]

That is what I have - RobbMc - zero issues. Also had problems with new Carter so I just stuck it in the shed!!

[shaker455]

Originally Posted by 72projectbird

So I picked up a 77 TA from GA. When it arrived the fuel pump was dead. Would run fine with the fuel bowl filled up, but the pump wasn't pulling any fuel. I hooked an electric Carter pump up just to get the car moving, and it worked great.

I just installed a new mechanical pump (Carter M6122) which looks just the same as original, with the larger canister, and return line output.

As soon as I installed it, the engine flooded immediately. I checked for a stuck needle, or sunken float, but everything is fine. When I went to crack the fuel inlet line on the carb, it was extremely pressurized. So I crawled under the car to see if the return was plugged, and when I removed the return from the pump it shot fuel out with enough force to cover the front disc brake.

I compared the old pump to the new, and the only difference I can see is that the return port on the new pump is the size of a pinhole compared to the original. I opened up the opening with the correct size drill bit, but it still is creating a ton of pressure at the carb inlet.

Is there something stupid I'm missing?

John & Ryan, check the fuel pressure with a gauge, most likely too much!
I had same issue with brand new pumps, no QC on new stuff

[Formulajones]

I was going to mention the same thing.

Anymore if I need a new fuel pump I have 2 options.

If it's a mechanical, I'm just buying the RobbMC stuff. The nice part is that they are all serviceable and he sells the kits for about $30. So if there ever were a problem they are easily fixed.

It's either that or I'm taking the plunge to do a baffled tank and drop a new electric pump inside the tank and be done with it.

Those are the only 2 ways I even do a fuel system anymore whether it's a stockish build or not.

[Formulajones]

On a side note since it was mentioned. Been a while but I posted a while back about the different brand stock mechanical pumps available and had pictures of 3 of them laid out. Airtex, AC, and Carter. All of them available at the local chain stores. They were all SBC pumps but still......

Laid side by side there is no longer any distinguishable characteristics between any of them. AC's no longer have AC cast into the body, they all had the exact same cad plating and finishes.. You literally can not tell one brand from the other once out of the box.

20+ years ago you used to be able to buy AC pumps that actually had AC cast in the body. Those have been gone for at least that long now. Ironically I'm still running one of those AC pumps on my Firebird that I daily as well as race frequently and that pump is going on 25 years old now. I'm at a point where I plan to change it out anyway as a preventative measure, (gotta keep it dependable) and will be installing a RobbMC.

In a nut shell, I really don't trust any of those chain store pumps anymore.

[OCMDGTO]

X2 on checking pressure. How about adding a regulator?

[tom s]

I have great luck with the Carters but never used on with a return.Tom

[Shiny]

Originally Posted by 72projectbird

...

As soon as I installed it, the engine flooded immediately. I checked for a stuck needle, or sunken float, but everything is fine. When I went to crack the fuel inlet line on the carb, it was extremely pressurized. So I crawled under the car to see if the return was plugged, and when I removed the return from the pump it shot fuel out with enough force to cover the front disc brake.

I compared the old pump to the new, and the only difference I can see is that the return port on the new pump is the size of a pinhole compared to the original. I opened up the opening with the correct size drill bit, but it still is creating a ton of pressure at the carb inlet.

Is there something stupid I'm missing?

I need to look at this soon, as I am moving forward to try and get my car running again. The last 3 attempts have ended with flooding. Like you, I verified carb inlet and float but still had flooding. I also suspected my pump was "overpressuring" the carb but don't remember residual pressure at the carb inlet. When I tried to measure the pressure, it jumped around and I never came to any real conclusion.

All the comments are insightful and appreciated. Comments about currently available mechanical pumps being a crap-shoot are not unique to this thread.

As far as "return line" and pinholes, I understood the return was for vapor only and not really designed to return fuel with any significant flow. Is this true?

As to remaining pressurized, I recall some discussions on the forum about "check valves" in the context of "drain-back" through mechanical pumps. The issue was hard starting from lack of fuel. You apparently don't have this issue but the discussion about pump design and integral "check valves" might be useful.

Please post more as you investigate.

Mike

[Formulajones]

Originally Posted by tom s

I have great luck with the Carters but never used on with a return.Tom

Are you using the high output Carters? I've used those in the past and tend to like them but that was a couple decades ago. They are on a different playing field than the stock replacement stuff I was referring to. There are also a few visual differences, at least the ones I've had in my hands anyway.

I'm currently running Summit's version of the high out put mechanical pump on the 56 Nomad which is a clockable body. I use it only to move the car around on occasion. It sits a lot with an occasional spin around the block. It holds a rock steady 8 psi cold and about 6.5 psi once warmed up, about what a mechanical pump should do anyway. The stock tri-5 replacement pump, made by Carter that looks like every other brand, would only hold 3 psi cold and once warmed up the gauge said zero, but it still ran and drove, although I never pushed it hard beyond 1/4 pedal because of the fact it showed no fuel pressure and I wanted to get back to the house. That pump quickly came back off.

[OCMDGTO]

Holley makes a decent mechanical pump, too. I can't remember if it has a return but it uses AN fittings.

[tom s]

Will need to look at the number,mine have been pretty solid at 6lb.Have a new one here that’s going on a 455 I have on the run stand now but it won’t be used on the stand.Tom

[Formulajones]

Originally Posted by OCMDGTO

Holley makes a decent mechanical pump, too. I can't remember if it has a return but it uses AN fittings.

Yeah that's what I ran on the Nomad for a dozen years or so back when it was my daily driver in the 80's. Those bodies are clockable too, a necessary thing on a tri-5 to make them fit.

Basically the Summit pump I have on there now is identical to the Holley Mechanical I ran, it's just half the cost. Holds the same fuel pressure I had back then. Basically just something I installed to keep the car mobile as the holley pump died from sitting a long time ago and the stock Carter tri-5 replacement pump wasn't worth a poop.

This is what I have on there now https://www.summitracing.com/parts/s...make/chevrolet Looks just like the Street Super Carter, Edelbrock, and Holley high output pumps they sell.

[Formulajones]

Originally Posted by tom s

Will need to look at the number,mine have been pretty solid at 6lb.Have a new one here that’s going on a 455 I have on the run stand now but it won’t be used on the stand.Tom

If it looks similar to the one I linked above, it's probably the Carter super street pump. Those are pretty good pumps, I think rated at 110 gph and hold 6-7 psi with no need for a regulator. Basically the same Summit pump I installed on the Nomad.

Worlds better than the chain store bought stock pumps that I've had very little luck with around here these days.

[72projectbird]

Originally Posted by shaker455

John & Ryan, check the fuel pressure with a gauge, most likely too much!
I had same issue with brand new pumps, no QC on new stuff

I'll be doing that today after watching the Patriots get wrecked by the Dolphins.

Originally Posted by OCMDGTO

X2 on checking pressure. How about adding a regulator?

I could add a regulator, but it's a bone stock resto deal, so it would look out of place.

[jhein]

I have a high output pump from BOP that I think is a Carter, but not sure. 120 gph @ 6.5 psi. So far, so good.

[Formulajones]

Yeah, if it's a Carter it would probably be the 6907 that Summit sells that Carter calls their super street pump. Same thing I mentioned above and I suspect what Tom is running as well.

Those Carter pumps work well and are completely different than the chain store bought stock type Carter pumps that look like your run of the mill cad plated sheetmetal bodies.

[tom s]

Yes 6907.Tom