Depending on the formulation of your local gas, 85 degrees could be hot enough to make it expand and overflow the vent holes. Is the leakage occurring after the engine is shut off?

Gasoline in Oregon, as an example, has a very low boiling point; I've seen it expand enough to come out the filler neck of both my 122S and 220 with a partly full tank. It has also seeped out the vent holes on the car with SU's, and the one with Mikuni's too, after the engine has been turned off.

The most effective thing I've ever done to reduce engine bay heat was to have my exhaust manifold ceramic coated; it makes a huge difference. I also head the heat shield ceramic coated.

I've got my fuel hose routed well away from the top of the cylinder head and covered with heat reflective sleeving, and a heat shield between the cylinder head and the fuel hose.

Of course, if the fuel pressure is too high, it will overpower the float valves, and you will get leakage. The only new fuel pump that seems to work correctly is the sealed Pierburg pump. The Skandix fuel pump has too much pressure for SU's, Mikuni's, Weber's etc. without the use of a fuel pressure regulator. Holley makes one that seems to be working for me so far. The adjustable chrome plated ones with the big dials (Empi, Mr. Gasket etc.) are prone to dangerous failure (fuel squirting leaks) and must be completely avoided for safety's sake.

Bill