Pre-war (up to 1942) Flathead Fuel Pump Problems

[39LaSalleDriver]

The newest wave of problems for my 39 LaSalle is a fuel pump problem. The car came with a Carter carb, mechanical fuel pump missing and port blocked off, Carter 4259 electric pump installed near the tank, and a cobbled together system of modern fuel lines and hoses.

Everything was running more or less alright so far as I know except the tank had leak(s), I didn't like the Carter pump (noisy, draws too much power, and terminals kept falling off pump), I want reinstall a mechanical pump to be the primary fuel source, and I want to properly redo the fuel lines with all steel, insulated, etc.

So I determined to revamp the fuel system. I have installed an all new tank from Tanks, Inc., purchased a mechanical fuel pump to be rebuilt (** see photos, I hope this one will work on my car), and installed a new Airtex E8902 electric pump. I will redo the lines when I am reinstalling the mechanical fuel pump.

This has so far gone okay except the car is now sputtering out somewhat and even having "coughing" or small backfires in the carb when a load is put on it (when accelerating, especially going uphill). To me it is acting as though the carb is being starved of fuel (tank is full). Admittedly, when I first hooked up the Airtex, the lay of the line wasn't  quite as straight as it should have been, and I didn't install a relay, and yes everything is properly grounded. Those things have been rectified, and while the problem has improved, it still persists.

Put pressure gauge on fuel line near carb and it shows 3.5 which "should" be enough, but clearly is not. I don't know what pressure the previous Carter pump was putting out (specs say 6), but was good enough that it didn't have these problems. I hate to do it, but I'm wondering if I should reinstall the Carter pump and live with it for now (which I don't really want to do), or buy an Airtex 8011 and install it with an adjustable pressure regulator.

A bigger issue I see is that if my current Airtex pump with a pressure of 3.5 isn't cutting it with my carb, will the rebuilt mechanical be under powered too? Perhaps I'm looking in the wrong place, and in fact the carb needs some adjustment which will allow a pressure of 3.5 to be sufficient.

Does anyone have any suggestions? Thanks.



** I purchased this mechanical fuel pump which was claimed to fit a 39 LaSalle among others. The only reference I can find to this model number of pump (1522119) is from an Australian site which offers rebuild kits which seems to confirm that it is appropriate for 1936-39 LaSalles. https://classiccarbs.com.au/index.php?_route_=Vacuum-Pump-Kit-Buick-Cadillac-Hudson-LaSalle-Terraplane-1936-39-Vac-side-of-dual-pump-900.080VPK-&keyword=1522119&description=1&model=1

Can anyone confirm that is model will work for me before I spend any more money on it to have it rebuilt?

[Steve Passmore]

That pump will fit but you may not be able to just fit a kit into it. (the link is only part of the kit) It's the early type with the flapper valves seating directly onto 89-year-old diecast which is sometimes not a good surface.    later ones had sealed removable valves. I would get that one p[rofetionally rebuilt where they can reseat the valve faces.

There's a myriad of things that could cause starvation, work you have done may have pushed something up to the carb? The pressure should be enough.

[39LaSalleDriver]

That pump will fit but you may not be able to just fit a kit into it. (the link is only part of the kit) It's the early type with the flapper valves seating directly onto 89-year-old diecast which is sometimes not a good surface.    later ones had sealed removable valves. I would get that one p[rofetionally rebuilt where they can reseat the valve faces.

Yeah, I knew that it was only the vacuum side. I just used that site because it was the only reference I could find to the type of pump I have. 

I'm wondering if maybe I'd be better off shopping around and picking up a later model pump and chalking this one up to "lesson learned" and trying to resell it.

I'm also beginning to wonder...is it possible that my starvation problem is tied into the same issue that my turn signals are having? Both are wired into the ignition switch. Could it be there is a fluctuation in the electricity which is causing both the turn signals and fuel pump to function erratically?

I would note that I have had a problem with my voltmeter fluctuating wildly anytime it gets near the car when it is running. Generator, regulator, battery, doesn't matter...I can't get it to zone in.

[Steve Passmore]

I have to confess to always using the later type.   Does sound like you have electrical issues.

[Tom Beaver]

Your voltmeter problem is probably caused by the EMF radiation from the spark plug wires.  I had the same problem trying to operate an electronic engine analyzer anywhere near the engine in my car when it was running.  Had to install EMF suppressing spark plug wires to get it to work.

Your fuel pump pressure of 3.5 psi should work.  You only need enough pressure to fill the float bowl and unless you have a major restriction in your fuel line that pressure is enough, that's all the pressure my system puts out.

Tom Beaver

[39LaSalleDriver]

The more I'm thinking about it, I suspect I'm going to be better off getting the later model pump. I see there's a couple of outfits that have pumps already rebuilt and ready to sell. Perhaps they would do a core exchange and I won't get hurt too bad.

Your voltmeter problem is probably caused by the EMF radiation from the spark plug wires.  I had the same problem trying to operate an electronic engine analyzer anywhere near the engine in my car when it was running.  Had to install EMF suppressing spark plug wires to get it to work.

Your fuel pump pressure of 3.5 psi should work.  You only need enough pressure to fill the float bowl and unless you have a major restriction in your fuel line that pressure is enough, that's all the pressure my system puts out.

Tom Beaver

Thanks for the heads up on the EMF business. All new to me, but as I have confessed before, electrical is not my strong suit 

I'm still concerned that something's not right though. Even though it "should" work, clearly the 3.5 psi I'm getting from my pump isn't good enough for my carb. Therefore, I must conclude that something is wrong there. Not in my immediate plans for right now, but I had anticipated having the carb rebuilt at some point. Much as I hate to, I may have to fall back and get an Airtex 8011 with regulator for right now to keep it running for the time being.

[39LaSalleDriver]

Did some homework on this as well as talked to a mechanic buddy of mine. He clued me in on an aspect I hadn't considered in this whole equation when he asked me how many gallons per hour my pump was putting out.

As I dug into the topic I found out that the Airtex 8902 (as well as the 8011) delivers at 30 gph and the Carter 4259 delivers at 72 gph. Quite a difference to be sure.

On top of that, I hadn't considered diameter of fuel line which apparently can make a decided performance difference. Now keep in mind, the fuel line that I have was installed by a previous owner and is a combo of steel and rubber tubing which in no way resembles the original system. In true shade tree mechanic fashion, I had opted to reuse as much as I currently had, as well as pick up some new rubber tubing for good measure to piece it back together until I can get a mechanical pump reinstalled. At that time I intend to install all new Nicopp line and route it as the original line was as much as possible.

Turns out the parts store had hooked me up with 5/16" rubber line rather than 3/8" line. There may have been some other 5/16" line already mixed in there as well, but I replaced it all with 3/8" line just to be safe. As of now, the situation has improved, but still stutters once in a while. Usually when I am in second gear hitting around 20-25 mph on an uphill incline. Sometimes it does it, most of the time it doesn't so I can't really pin down a more solid pattern. Since my area is relatively level with some small rolling hills; and I don't trust it yet to take it out on the highway (I live in a metropolitan area) that's about all I can report at this time.

I think for right now I'm going to leave everything as is, get a newly rebuilt mechanical pump put on, put in all new Nicopp fuel line, and see what happens. Since I hope to only rarely have to use the electric pump, I am hoping this will suffice. If not, I think I will reinstall the Carter pump in parallel, put in an adjustable regulator, and see if that cures the problem.

Thanks for all the suggestions and help and I may have to revisit this topic in a few weeks when I get all the new gear ordered and installed.