Today I installed a Mr. Gasket Advance Curve Kit (mrg927g) on my 1971 Corvette. The instructions were OK but they didn't provide any information about the advance curve you would receive by using the enclosed black, silver, and gold springs. Nevertheless, I installed the enclosed centrifugal weights and started with the black springs. When I checked the timing, it wouldn't advance at all. After removing the distributor rotor to see what was going on, I discovered that the Mr. Gasket weights were made too big and they actually butted up against the square locating pin of the rotor. After comparing the original weights with the Mr. Gasket weights, it was easy to see that the original weights were made thinner especially where they fit around the distributor shaft. Just to make sure, I weighed each weight both from the Mr. gasket set and the originals and they weighed the same @ .6 of an ounce. So, I used the original weights and the Mr. Gasket springs. It turned out that even with the strongest springs from Mr. Gasket, all of the centrifical advance was in by 2000 rpm. Basically, I wasted money buying this kit as nothing worked as advertised. I found some original GM lighter springs and used them. This worked out well as now all of the centrifugal advance comes in right about 2900 - 3000 rpm. I am posting this note so that others thinking about using the Mr. Gasket kit won't waste their money.
Mr Gasket parts like this have been made in China for over 10 years now, pure JUNK! MSD uses same weights in their distributors and they have decent kits or Mallory might have something still. Also ISKY cams had a great kit but, I haven't looked for one of those in over 20 years and they may be gone from their catalog now, MSD is your best bet.
Hear ya brother. I tried all the springs in the 928G kit and in different combinations with no luck. What I noticed was they were all advancing at idle and coming all in way too early. Went back to the original stock springs. I sure wish somebody around here had a Sun machine and lots of original weights and springs because I don't like trying to set up the distributor correctly in the car.