Hi Neil:
What you are asking about has been a VERY common modification to carburetor installations to even out the fuel pressure fluctuations "seen" by each float chamber. This is accomplished on Webers by installing a double-ended banjo fitting to the other two rearward fuel inlets and running a piece of fuel hose between them. Those fittings are now quite difficult to find anymore but this does help and its worth the effort.
I'd also add that you really must have the insulator kit installed between the heads and manifolds to help the prevent heat soak and fuel percolation that is the root cause of your problem.
Needless to say, I've assumed here that your float levels are absolutely PERFECT.
