Air flow balancing - demisters

[dave295]

Restricting the airflow on the drivers side with a pipe or tubing inside your manifold might help.
Where Dave H. drew the red line in the above, block the manifold with a piece of cardboard. Knock a circle out of it, say the diam. of a toilet roll tube. Do the same at the other end so it resembles a dumbbell or a H shape. Varying the pipe length would hopefully vary your pressure and be adjustable.
Or a pipe running directly to your vent inside the manifold and sealed around the middle of the manifold (give or take) from pipe to edge of manifold might help.

Dave