These carbs MAY be jetted a little rich, but the real reason for crappy mileage is TOO MUCH FUEL PRESSURE.
I agree with Mitch, once vapor pressure is relieved the gas should stop flowing. How much of an incline is it? It could just be a simple siphoning action. Siphons work pretty well once started.
Your fuel pressure is too high, and your float valves need to be replaced. You may also need to vent the tank. Do those three things. All three.
I'll say it one more time for it to sink in. 1.5 PSI, no more for EMPI/Solex/Kadron carbs.