Thanks Ron, I do realize that this is not the end. But since my vanishing fuel has been such a nightmarish snipe hunt, I thought I'd report the TENTATIVE improvement.

My gauge is fairly reliable. I've been watching and counting miles for several months As I told George, I have a good sense of my fuel/consumption and the accuracy of my fuel gauge. I also removed and rebuilt the gauge when I bought the car, so I know what is going on in there.

Both my mapped (recall that I am a geographer) and my odometer read mileage shows a 15 mile commute each way. 30 round trip,


I ran out of fuel once at half a tank because my in-tank pickup tube was broken off. Chris Horn sold me a decent replacement tank - that aside from shedding a little crud from new gasoline, has been trouble-free. I've had this tank completely empty. It also has tar undercoating on it, which would very clearly show a fuel/tar solvent leak.

Until the weather recently warmed up, I've had to drive the car with heat on and from my previous experience with my old rusty 145 (1994-1998), when you are running with the heat on, you don't get outside fumes sucked into the cabin.
I'm not going to concern myself with the science there, but I've consistently observed that correlation.

So, with the weather warming, I've started to smell some exhaust and some fuel in the cabin. Nothing like you would expect if you were dumping 5 gallons of fuel out a leaking fuel line, but something...

I'm still chasing carb tune, but I think vacuum leaks may have been contributing. I noted that my manifold has small cracks at the two intake ports. I think I way over-toqued the vacuum fittings trying to get them sealed up last year. This must have caused stress and led to the formation of small cracks. I'm trying out a nos aluminum intake that I got some time back.

I should again point out that I had done nothing to fix the vacuum or to the 3-bolt carbs when the economy began to improve.

My working theory is that it due to a combination of vacuum leak/carb tune and the connector hose from the tank line to the fuel pump. I did have 5/16" ID tubing clamped on there, but have now gone to 1/4" ID tubing. Fuel seemed to vanish most quickly under load on the highway. When I was running a higher pressure pump, fuel was lost that much faster (I lost an extra 3 mpg).

Then again, I've still no idea why I could not find a leak while running the engine at high rpms in neutral. Lots of unanswered questions remain.

For now, I'm going to try the new manifold setup with the new hardline and just the pump filter. I'll provide a proper calculation when I fill up next.