Fun with fuel tanks

[Keith]

I haven't been posting here much - the MG's been sitting partly due to some fuel problems and also because I was running a V8-powered Miata in the Targa Newfoundland. But it's time to get back on it.

I'd been considering building a new tank, but the stock one fit so well under the car I figured I'd see if I could do something with it. So I pulled the tank out and opened it up.

To keep from blowing myself up, I filled the tank with water before using a sawzall to cut the top off. And was I surprised at what I found inside! This is the top of the tank, placed upside down on the driveway.



Check out that big canister...thing. I popped the four spot welds holding it to the top of the tank, here's what it looked like in place.



The MG is a 1972 model that I got out of California. It had a charcoal canister setup, and that's the line to the charcoal canister you can see in the first picture. The line ran between the canister and the top of the tank and breathed through a really small orifice at the top of the canister. There's a round hole in the bottom you can see. A dent in the bottom of the tank (I'm thinking someone tried to use it as a jacking point) was perfectly placed to block this lower hole off. So it was basically a giant empty cylinder in my tank.

The problem? I'd been using that charcoal canister line as my fuel return line for the fuel injection system. It's a wonder the poor pump managed to push any fuel back into the tank at all. It would have been squeezing it out of the grooves on each side of that canister at the top of the tank.

I decided to address all of this by building new pickup and return lines, using the big canister as a sump of sorts.



I cut the top off the canister and enlarged the bottom hole considerably. I flipped it over, cut a few slits in the (now) bottom and bent the resulting "doors" inwards a bit. The new pickup line was bent up out of 3/8" brake line with a 5/16" return - they also dodge around the fuel level sender, thus the odd routing. The return dumps back into the sump, aimed at the side of the cylinder so it'll swirl into place. The previous charcoal canister line was cut off and capped. I also beat the big dents out of the bottom of the tank.

There's an added trick in here. There's a baffle that runs from front to back on the tank. The float for the fuel sender is on the side away from the pickup. But the hole in the baffle is about 2" off the lowest point of the tank. So when you get down to your last gallon or two of fuel, it no longer gets transferred to the other side of that baffle...where the pickup is. At a certain point, the fuel gauge would stop going down as you continued to suck the fuel out of the tank. There's no good final result here. It's like they wanted you to run out of gas.

A few holes at the bottom of the baffle avoided the sneak "out of fuel" attack. Seriously, who thought that was a good idea?


Welded it all back together and voila, a new fuel tank! I ended up having to go back into it later because of a pinhole in the feed line that had the pump sucking air instead of fuel - should have pressure-tested that before assembly. Whoops. The tank is upside down here.


I also had a problem of spitting a bit of fuel out of the filler neck on track. The filler neck is right above one of the mufflers, which led to some exciting moments.


The solution was to put in a flapper from a modern filler neck. I cut one out of a Miata filler and welded it into the neck for the MG. I'm hoping that will solve the problem. The future will hopefully bring a cool Aston filler neck setup, but not yet.


Thanks to all this I have an enlarged tank capacity (in large part due to the removal of the big sealed canister taking up space), an improved pickup, better baffling, fewer fireballs and (hopefully) no weird fuel delivery problems. Time will tell!

[Moderator]

Keith, it's great to see you back!  I thought this was supposed to be Janel's car.  Isn't she driving it much?

I'm always amazed how quickly you do things and how easy you make everything look. Real talent! Like, for example in this case, welding rusty oily painted steel... but I don't know why you bothered. New MGB fuel tanks are so very, very cheap (<$200) and they're made from "Ni-Terne" (nickel coated then zinc dipped) steel. If you search this site there's a pretty nifty article about putting an in-tank EFI fuel pump in one. (Bonus: better fuel sender.)

Now that flapper idea is neat. - I'm gonna have to steal that! - I spilled fuel from my cap while we were autocrossing at the BV8 meet. Also, the flapper should eliminate splashing when topping-off at the gas station. Great idea.

[Keith]

After the car blew a big fireball on track and then died on the side of the road on the way home, Janel wasn't too interested in driving it for a while. It's just been sitting while I got other things out of the way.

Welding the tank wasn't that big a deal. I cleaned the seam down to bare metal with a wire brush. You don't really want to be welding on zinc plating, either, so the original tank was a better choice in that regard. Besides, I like having the drain plug - and I figured that if this one didn't work out, I could go with something else. There wasn't any reason to buy a $200 tank when I had one for free that didn't need any more special attention than a bit of whacking with a hammer.

It really doesn't take long to do stuff like this. Most of a day for the first time, including running around picking up things like the brake/fuel lines and reworking my current fuel feed routing outside the tank. The second time - to fix the pinhole in the pickup tube - was about 2 hours from starting to drain the fuel to bolting it back in. The guy who designed the exhaust system made it fairly easy to remove the back section

We'll see how well the flapper works. I'll have the car out on the road tomorrow. Short trips only at first until I'm confident everything's working nicely. There's more serious work in the car's future, the transmission has to come out to fix a reverse shift fork and also to add 1/4" of clearance between the bellhousing and one little bump in the tunnel that's causing a big vibration. Yay!

[NCtim]

Hey Keith,

Sure is nice to see you back. I originally found this site by reading your Slow-Car-Fast blog. Thanks for that!

Nctim