I tried that and it didn't work. The carb is attached to the inlet manifold which is generally fairly cool due to (a) the rush of cool inlet air and (b) the latent heat of evaporation of the petrol in the carb. Putting on a thicker (or doubled-up) gasket slightly reduces heat conduction but the latter is not great anyway.
The problem arises from radiant heat from the (hot) exhaust manifold being transmitted directly across the air gap from the manifold to the carb and heating it up. In my experience shielding the carb from this as described in my previous post was the only thing that worked (albeit only partially).
Normally this only happens when the car is standing, This is because when you're actually running the engine the carb is cooled by evaporation of the petrol from the main jet. When you stop, no flow of petrol - no evaporation - no cooling. In addition there are no cooling draughts within the engine compartment. The residual heat from the exhaust manifold and engine block radiates to the carb, heats it up and the rot sets in.
Either all the petrol boils off (in the case of my old 845cc with a small Zenith 281 carb) or possibly only some of it (in the case of your GTL). Curiously, my late-plate (1984/5) LHD 845cc does not suffer from the problem. Possibly this is because it has a huge Solex carb (factory standard) which takes more heat to get up to petrol boiling-off point than the smaller models.
As an 'Elf 'n Safety point, if petrol is evaporating from the carb, it must go somewhere. The implication is that there may be a fuel-air explosive mix within the engine compartment for a short time after the car is parked, until normal breezes blow it away. Moral : don't ever lift the bonnet with a fag in your mouth, particularly in the few minutes immediately after a run.
