Sorry to dig this one up, but it needs for sure clarification.
However I think that retaining a degree of springiness may be a good idea at the very top end, but when talk is made of large shims, surely the main is nearly coilbound anyway? Hence others just fitting a solid spacer and job done...
What exactly would shimming the main completely do? Because in some pictures..
This picture clearly shows that the main spring only has about a few mm of travel before the two spring seats meet.
This picture shows that three small washers easily takes up all the space and eliminates the main spring.
This picture shows a solid shimmed main, and roughly 4mm of shim on the intermediate spring..
It looks as though the main spring is completely out of the equation without any shimming at all, as 3mm disables it. the intermediate spring is then shimmed with 3-4mm itself, and looks as though before being completely coil bound it can only move around 3mm.
It is almost a solid governor! Would this car have had driving problems? The intermediate spring looks fairly strong, this car would rev in almost an instant... from what it looks.
So my question is, what is the best method? From what I can see, the main spring only moved 3-4mm.. shimming it that far disables its function... shimming the main spring anymore than that would effectively be putting a pre-load on the intermediate spring.. as the left side seat is stationary to the cage.. it can only go left and compress the intermediate spring...
I (among many other I'm sure) am looking for a definite answer as to what the correct shimming is for best driveability/performance factors.. I have an old pump here, I may tear it down tomorrow and do some investigating on the Governor cage.. but won't be able to install it to test it on a running engine.