Adjusting/recurving vacuum advance

[german240]

Hey guys, 

is there a how-to recurve the Datsun vacuum advance mechanism? What are typical target values? 
I got a remanufactured Cardone ZX dizzy and would like to play with it a little bit. 

As far as I understood, there are two screws: 

- Inner screw for maximum advance (CCW for more maximum advance?)

- outer screw for vacuum setpoint to start advance (CCW or CW for sooner start of vacuum advance?)

[narth327]

http://newprotest.org/projects/510/jasonGrayDistributor.pl

[grannyknot]

 

Taken from the link above,

Vacuum Advance

You should have a functional vacuum advance canister for street driving. The vacuum advance canister alters the ignition timing in response to engine load. The vacuum canister does not produce advance under full throttle operation, manifold vacuum is much too low so canister shouldt effect tendancy for engine to ping under full load.. Under partial throttle operation, on the intake stroke the piston pulls against the blockage of the throttle plate so vacuum is produced in the intake manifold and the cylinder receives less than a full charge of air/fuel and retains more of the burnt exhaust gas in the cylinder. This causes the fresh (partial) intake charge to burn slower when ignited so earlier ignition is needed to extract maximum energy from the fuel. Not using vacuum advance will give you no real increase in performance and will decrease your gas milage and increase emmisions unnecessarily for street driving. The vacuum advance canisters can also be recurved. All the EI dizzys use the same canister that is adjusted at the factory for desired advance characteristics. To re-adjust, remove the putty blob on the end of the canister with a high speed grinder to expose the adjustment screws. Inner coaxial pin limits vacuum advance travel, outer grub screw adjust the spring pre-load on the diaphragm. Turning the outer screw counterclokwise reduces the amount of vacuum necessay to initiate advance. If you are using sidedraft carbs and the vacuum signal is decreased, use a gauge to measure vacuum under cruise conditions and then re-set the advance canister to give full advance at this vacuum level. It may take some trial and error to find the correct amount of vacuum advance, I would think that between 15-20 degrees (crank) at 10-15 in Hg would be a good starting place. Advance beyond the initial + mechanical limit of 36 degrees is needed with under high manifold vacuum (low engine load). For each 1mm of travel of the vacuum canister actuating rod, the timing is changed by 4.24 crankshaft degrees. Once you have finished adjusting canister, you must re-seal the threads of the adjusment screws with paint or hardeing silicon putty or air will leak past the threads

Edited July 9, 2018 by grannyknot

[german240]

Thank you! I knew I've read it somewhere, but couldn't find it ?