Austin Seven Distributor Advance Curves
The blue curve above represents my starting point. This is the original distributor using 60+ year old springs but with new bearings and play removed from the advance mechanism itself. As one can see most of the advance is taken up just coming off idle rpm's.
The red curve shows the improvement gained by using new springs (I was lucky to find some "new old stock" springs for this test). Road testing showed a marked improvement in performance over the first settings. The Lucas part number for the replacement spring set was 416042/S.
The yellow curve is that from a Bosch distributor as modified by the Austin Seven Club of Victoria. They have spent some time in improving the curve for current Octane levels (96?) etc. Their curve clearly gave an improvement over the rebuilt DK4A distributor. The Bosch product is much easier to calibrate. Additional advantages are that it does NOT have a fragile base (most DK4A bases are showing there age), new consumable components are cheap and readily available. In Australia a second option has been to modify 1959 VW Bosch distributors but these are increasingly difficult to obtain. The Bosch 062-406 Distributor was used on a range of car models over the years. I have recently purchased one from the wreckers that was off a 1971 Toyota 4 cylinder model. Mounting modifications are simple and basically involve cutting a second "O" ring groove, making a distance spacer, cutting the drive shaft shorter and fitting an Austin Seven distributor gear. After this the distributor should be recalibrated to the yellow curve above.