My 72 Bavaria with the original M30 has the original points type distributor but with Weber DGAS 38/38 carbs.
The vacuum advance/retard as I bought the car was hooked up like this...
Manifold vacuum to the retard port on the dizzy. Single vacuum line off the rear carb manifold to the dizzy.
Ported vacuum to the advance port on the dizzy. A vacuum line from the ported vacuum connection from each carb, connected with a "Y" fitting then on to the advance port on the dizzy.
I've read here that the retard portion of the system does not enhance running or driveability in any way and to disconnect this line and plug it at the manifold. True this?
I can't see a good reason to have the ported vacuum ports on the two carbs connected. Is there a good reason for this or should I just run the advance off of one carb?
The consensus here is to run the vacuum advance off of ported vacuum. However, in the broader old car hobby there seem to be as many arguments to use manifold vacuum as ported vacuum for the advance. The vacuum signal is going to look the same to the dizzy after the throttle plates uncover the ported vacuum port so the difference is essentially that manifold vacuum picks up the signal at idle and ported vacuum doesn't. At any other high vacuum condition ported and manifold are seeing the same signal. The manifold signal at idle will likely increase the idle speed.
I will probably experiment with both manifold and ported vacuum to see what (if any) the differences are. Has anyone done this experiment and if so, what were the results?
The vacuum advance/retard as I bought the car was hooked up like this...
Manifold vacuum to the retard port on the dizzy. Single vacuum line off the rear carb manifold to the dizzy.
Ported vacuum to the advance port on the dizzy. A vacuum line from the ported vacuum connection from each carb, connected with a "Y" fitting then on to the advance port on the dizzy.
I've read here that the retard portion of the system does not enhance running or driveability in any way and to disconnect this line and plug it at the manifold. True this?
I can't see a good reason to have the ported vacuum ports on the two carbs connected. Is there a good reason for this or should I just run the advance off of one carb?
The consensus here is to run the vacuum advance off of ported vacuum. However, in the broader old car hobby there seem to be as many arguments to use manifold vacuum as ported vacuum for the advance. The vacuum signal is going to look the same to the dizzy after the throttle plates uncover the ported vacuum port so the difference is essentially that manifold vacuum picks up the signal at idle and ported vacuum doesn't. At any other high vacuum condition ported and manifold are seeing the same signal. The manifold signal at idle will likely increase the idle speed.
I will probably experiment with both manifold and ported vacuum to see what (if any) the differences are. Has anyone done this experiment and if so, what were the results?