Correct, just the one electric pump. The pump is new (replaced before leaving Alaska) and the fuel system was gone through thoroughly before leaving, to the point of pulling and steam cleaning the inside of the fuel tanks and under anything other than low speed high workload situations (climbing a long steep hill) everything works properly.

I know why this causes vapor lock (lots of heat generated by the engine working hard coupled with lack of airflow to dissipate the heat due to low vehicle speed) but what I really need to know is this: Is the vapor lock on the output side of the fuel pump where all the heat is, or on the input side of the pump where there is little heat but which I had understood to be the only place vapor lock could occur?

Perhaps a fuel system upgrade is in order--replace the fuel pump with a recirculating pump, the kind that recirculates back to the fuel tank the fuel that doesn't go to the carburetor so that there is always cool fuel in the lines. But this is complicated by the dual tank setup; I'd have to choose one tank or the other as the default recipient of the recirculated fuel. This could work very badly if both tanks were full and I was taking fuel out of the non-recirculated tank.

Hmmm... this gets me to thinking. How about a simplification of the whole system, like the attached? OK, it's not a simplification, is it? I get rid of one component (switching valve) and add a bunch of other things, but as a scatter-gun approach to solving the problem it ought to be sure-fire. I like the fuel pump redundancy idea, too. If one pump fails, I can continue on the other one. Center-off position on the SPDT switch also gives me theft protection, because God knows, the car thieves are out in force looking for 1971 school buses!

Are the check valves necessary, or are they built into the pump(s)? I don't want fuel recirculating to any tank other than the one that fuel is coming out of in order to prevent overflow in a full tank.

One problem I foresee is finding someone to do the work. Most mechanics are reluctant to work on fuel tanks, particularly if welding is involved, and I think there would be welding required to install the return line fittings to the tank. Are there any magic fuel-resistant epoxy adhesives that would work? I've used a fuel tank leak repair epoxy that worked for years after the repair. Could I drill a hole in the tank, thread a fitting into the hole and then gloop the hell out of it with epoxy? [Gloop = mechanic's technical term]

tanstaafl.