NEGATIVE EARTH ONLY..Reproduction CONTACTLESS Distributor suitable for modern day fuels for 850 and 998cc pre 1974 with upgraded rotor arm "Negative earth only". A worn out distributor can cost you both performance and economy. Precise spark timing and distribution is the job of the distributor. Merely replacing the points and condenser will not fix the chronic problem of worn out bushes and shaft. These look like the originals apart from vac unit which has later push on connector.
Most A-Series cars had a vacuum advance distributor, only the Cooper "S
12G2140 had a full centrifugal version. The vacuum is designed to retard the timing under heavy load thus decreasing the chance of detonation. These units are guaranteed to out-perform your old tired version. The best test is to put a timing light on your car and watch as timing marks on the flywheel dance and bounce around as the engine changes speed, etc. Install a new distributor and try it again!! All the bounce will never go completely away as long as you are driving the distributor through a timing chain gear set to the crankshaft. Timing is ideally set by the crankshaft and thus unless you setup a "crank-fire ignition" some bounce will always be present! As little as possible is the best we can hope for!