MG Car Repair: Vacume advance on carb 1979 MGB-LS, manifold vacuum, vacuum advance

Question
Just noticed today that the vacuum advance hose to my distributor is not on and the port on the manifold where i think it is supposed to go is plugged. My car is idling high. Does the vacuum being off the Distributor have any affect on idol speed?
Thanks,
Steve

Answer
Hi Steve,

Yes, a advance system not connected can change idle speed but first you need to ID the distributor advance system as a vacuum advance unit or a vacuum retard unit. It is easy to do on an MG, just look at the vacuum port on the diaphragm. Is the port on distributor side of the diaphragm or on the side away from the distributor? This only applies to MGs. If the port is on the distributor side of the diaphragm it is a retard system and it must use "intake manifold" vacuum and does affect idle if removed. If it is away from the distributor it is "Ported" vacuum and must use vacuum from a port on the flange of the carburetor which only applies vacuum when the throttle is open. This type does not affect idle.

Howard