MG Car Repair: Vacuum advance, hand operated vacuum pump, thumb nut

Question
Good morning,

I suspect the vacuum advance is not working on a '80 MGB with a Weber conversion. The conversion has been on for 25 years with no problems. How do I test it and if need be, how is it replaced. Hopefully the distributor does not have to be replaced with it. Thank you.

Answer
Hi Doug,
You need a hand operated vacuum pump called a MityVac or any vacuum pump with a gauge on it. Just pump up some vacuum and watch the advance plate move. Then stop pumping and watch to see that it holds a steady vacuum.
If it is bad you can usually find a replacement at one of the MG parts suppliers like,  Ingel Imports, The Roadster Factory, Moss Motors, British Parts North West or Victoria British to name a few.
They all have web sites and toll free numbers. (you may need to give them the number off of the distributor.
Removing the unit from the distributor depends on which you have. If it is a 45DE4 you need to drive out the small pin near the vacuum unit and disconnect the rod from the points plate. If it is a 45D4 it is obvious, just remove the screw from the side of the dist. If someone has installed an older dist you need to just remove the small lock on the end of the threaded shaft and unscrew the thumb nut and disconnect the rod from the points plate.
Howard