After reading recent very helpful posts on recurving distributor advance I've decidied to have a go at this myself. I've set the plate to the 13L tag and fitted lighter 925D springs and now come to adjusting the vacuum advance.

It's a '57+ unit with an allen key through the cannister adjuster. My question is does this limit the amount or just the rate/speed of vacuum advance?

Thanks

Richard

The Allen key adjustment controls the amount of advance.You can control the rate of advance by using a restrictor in the vacuum line.An electrical butt connector(red) can be used.By crimping the connector you can change the size of the opening. Try a couple of sizes and se how it works.You should be aiming for 8-9 degrees vacuum advance.Total advance should be 44-46 at the crank all in by aboiut 2800 RPM..If you set the initial timing at 10 plus 8 plus 26 centrifugal gives you 44 total advance.Dont forget that at cruising speed when vacuum is high the vacuum advance will come back into play.I didnt know that myself until I did some reading on the internet about timing mods.You can also play with the centrifugal advance by using the 2 light springs and bend the anchor posts slightly through openings in the breaker plate.You might try one original spring and one light spring and see if that makes a difference.Just adjusting the vacuum can and using the light springs will make a noticeable  difference.Have fun.A suggestion.Before you start trying to adjust the vvacuum can,squirt some WD-40 or similar into the opening and let it soak a couple of times before you try and adjust it.The screw tends to seize up and you dont want to strip it.

  

The adjustment screw inceases the spring preload against the force exerted by the vacuum diaphragm. As this preload increases - advance travel at any given vacuum level decreases. I'm reasonably certain that the increased preload would also try to increase the rate at which the pot's operating rod would return if vacuum were suddenly decreased  

When its all the way clockwise (CW) - seated - the screw has the least effect on travel. As you turn it counter-clockwise (CCW) the preload goes up. Just don't over do it in either direction - the threads are small and strip easily.

The butt splice inserted into the vacuum hose allows "tuning" the travel speed by making the vacuum pot act as a "dashpot" as well.

 
 Steve Metzger       Tucson, Arizona