When I was unable to successfully rebuild the OE Zenith carburetors on our BMW Bavaria (no patience), I bought a pair of used Weber 32/36 DGAV carburetors (with the linkage and a manifold) on eBay for $99. I bought rebuild kits and some new jets from Pierce Manifolds (because they’re sort of close to me).
For some reason, I also decided to replace the mechanical push rod driven fuel pump with an electric rotary vane pump.
I found that Top End Performance had a discourse on the Carter 4070 fuel pump saying it was a good pump for Weber carbs. I first mounted the fuel pump on the firewall, near the overflow tank.
On the highway, I noticed that the car would occasionally stutter and I realized that the engine was becoming fuel starved because the pump was designed to be more of a pusher, closer to the gas tank.
I moved the fuel pump to underneath the car, just forward of the fuel tank. I used a Napa 1814U “Quiet Pack” that mounts the pump on rubber bushings to isolate it from the car’s frame and ran the 12v+ for the pump from the fuse box.
I also bought this Holley shut off switch that works off of engine oil pressure. Joe Weir, on the Senior Six Registry mailing list sent me a diagram that uses a relay (12 63 1 276 165) from a 320i for fuel shutoff.
The only problem I’ve had is with the electrical connections to the pump falling off – they’re held on by friction. To resolve this, I put a dollop of JB Weld on each terminal, then stuck the connectors on.
17 Replies to “BMW Bavaria + Carter 4070 Fuel Pump”
I am about to install this same fuel pump in my 72 Bavaria. Thanks for the write up and the pictures, they have been very helpful in my planning.
I have one question – It looks like you modified the steel fuel line to accommodate the pump in its location. In the second photo, did you cut the pipe to divert the fuel flow to the pump? It seems that way, I just want to make sure.
I’m assuming all these cars have the same layout. Looking at mine, the rubber hose attaches to the hard line at a connector mounted on the wall of the wheel well.
Thanks for your help. Can’t wait to get this one reliable again, I have another Bavaria that I have put a ton of work into that I will probably part with soon. Seems silly to keep two of the same car. But they do look pretty sitting together.
Again, many thanks for your blog. It has been a great help.
Andy, it’s been 10 years since I did this but I’m pretty sure that I just added rubber hose connected to the hard line to get to the fuel pump.
No problem, Leslie. I appreciate your reply. Thanks again.
Hi Leslie; I am about to replace my mechanical fuel pump on my e3…curious to know where you located the Holley oil pressure cut off switch…did you Replace the original oil pressure sensor with the Holley? Or is there another port you were able to use? Or did you add a tee and keep both sensors in operation?
Moses, I never got around to installing it. I looked at T-fittings and it seemed that if it were screwed into the oil pressure switch location, that fitting and the two switches would stick out kinda far at that point on the head. I probably would have used the fuel pump relay.
I am wondering what sort of mileage you are seeing from this setup?
My car returns 15mpg fairly consistently around town with these carbs, but I am hoping to improve this figure.
Ben, I was getting 12-14 mpg around town. From what I have read, 15-17 mpg in the city with Weber 32/36 carburetors were about the best numbers I’ve seen.
I have Webers on my 72 Bavaria. I have a fairly generic Purolator electric pump installed in the trunk just north of the fuel tank. Today it died on me… it blew a fuse, and the replacement. I think the pump just gave out–it was previously installed in the engine compartment but made such a terrible racket I had it moved to the trunk. I’m encouraged to hear about this pump designed to be in the trunk–I think mine gave out like a weak heart.
Have your Webers been rebuilt? It sounds like there is some kind of air leak. If the base of the carburetor or manifold isn’t flat that could cause the problem.
Also, if the throttle shaft is worn, air will be pulled in through the leak and cause that.
See page 4 of this Weber Troubleshooting Guide. While the engine is idling, spray carburetor cleaner on the outside of the carburetor and intake manifold. If there is a vacuum leak the idle speed will change.
I’ll take a picture of my setup later and post it.
I have a E3 3.0S. I have also purchased a pair of Webers to replace the OEM Zeniths. After installing on the factory manifolds, I am having problems with the rear carb, fuel drips from the Venturi tube, mixture enriches and I get continuous stalling. I am sure it is not a carb issue since I have them interchanged and always the carb put at the back becomes problematic. I suspect of the vaccuum circuit. It is as if the rear carb is not vaccuum-operated so fuel level grows at the top. I would appreciate your comments on this. If only you could post a picture of you vacuum circuit installation, that would be superb!
Summit Racing seems like it will ship to Australia for a $ AUD 28 additional handling charge.
I have a 1976 E3 3.0L. Whilst the carbys work well I am having trouble with the mechanical pump.
I will make enquiries in this country about the Carter unit.
Thanks, Regards Jeff
The oil pressure shut off switch is for safety. I looked at that inertia switch too. Joe Weir, on the Senior Six Registry mailing list, gave me a BMW fuel pump relay part number (12 63 1 277 245, about $35-40) and Bill Gau gave me a wiring diagram for the car. The relay is connected to the ignition and fuel pump – so when the ignition is off, no power to the fuel pump. I have the diagram somewhere, I’ll put up a link to it when I find it.
I bought the Carter 4070 pump from Summit Racing Equipment for $ (US) 72.00 based on the comments in these notes at Top End Performance. As I said, I think it is more of a "pusher" type pump, so it should be mounted as close as possible to the tank, not up near the carbs, where I put it the first time.
hi! clean installation u got there. i was hoping to buy a carter p4070 electrical fuel pump. can u give me more info about it? im using a weber 32/36 2bbl downdraft conversion kit for my mazda pickup..
Craig, your project looks like more than I could handle. I started with a pretty decent car and that was too much for me.
Jason, I thought about an inertia switch because my Alfa has one too. Thanks for the suggestion.
The shutoff switch is more of a safety mechanism, correct? Another option would be an inertia switch out of a fox body mustang. They’re located right under the driver side kick panel if you want to grab one out of a junkyard. Using both the oil pressure and inertia switch would be safer than neither I’d guess 😉
Very clean installation. I would never have thought to add a shut off switch. I’d like to think I would notice the oil pressure issue and shut it off myself but I guess the shut off provides a little insurance for inattention or if someone else is driving. Reading your updates helps keep me moving on my own Bavaria projects. I need to update my website but I have made more progress.
I followed your link from SSR email.