MGB Register Forum

I believe Vic has noted that the base plate only moves with the vacuum,NOT the weights?

Ian F

True Ian. I've got a distributor with no vacuum advance and it obviously doesn't have a moveable base plate . With the distributor fitted you should be able to turn the rotor arm a fraction counter clockwise against the springs of the centrifugal advance and the rotor arm should spring back unaided to its original position if the springs are working.

I misunderstood Vic... learning stuff here.So as you say, it all points to the vacuum/ baseplate movement being the area of concern. Ill look into this in the week..fingers crossed

Just been out to the garage and dug out a very old original Lucas distributor, dismantled it and it is just as you describe.
I have to confess that I've never been unduly concerned or had much difficulty with my original set-up (hence my lack of knowledge!). I have dismantled and cleaned many, but obviously never retained the understanding of exactly what moves and when!
I took Peter Burgess's advice and used a standard original Lucas unit, rebuilt by the Distributor Doctor, ensuring I had circa 30 degrees max advance. I have fine tuned the advance a little to just remove any pinking under full load from low revs.
The DD is highly recommended!

Ian F

One further thought for Andy(?), if you are using one of the newly manufactured distributors (available cheaply from many MG suppliers) I would recommend throwing it away!

I did try one of these a few years ago and it was quite impossible to set up correctly. I suspected the cam was the wrong profile, and I have been told that the advance curves are generic and not tailored to any specific vehicle. The supplier was generous enough to give me a full refund, after which I got an old original Lucas unit rebuilt by the DD. Never had any problems since and it certainly improved the performance of the B.

Ian F

It is worth checking that the vacuum advance pipe and the rubber connectors at each end are in good condition. The connectors sometimes split allowing air to be drawn in.

The centrifugal advance does not move the baseplate, it moves the 4 lobed cam relative to the input driveshaft. The vacuum does however move the baseplate. The suggestions from others that the fault is with the low tension wires inside the distributor seems like a good one to me. I've noticed that the wires to the pick up on electronic contact breakers are a great deal stiffer than in a points distributor. I have been given a Luminition Magnetronic pick-up but unfortunately it was off a 45D distributor and the fitting kit to make it fit my 25D is £41. The cost and the worry about the LT wires are reasons why I haven't fitted it yet. I'm fed up with faffing with points though.

Mudguardandy.
It might be worth taking the distributor cap off and manually move the moveable base plate clockwise and watch what happens to the LT wires. As Paul H says they tend to be stiffer than the points wires.
Paul, I had a Magnetronic ignition for a 45D4. I lost the small base plate fitting kit so I rang Lumenition and they sent me a freebie.

I have manually checked the movement of the base plate, also sucking the vacuum hose operates everything as it should. Checked hose connectors at each end.
I have a new set of points on the way so will fit them if nothing else works, though the electronic module worked great and was totally reliable...also not a fan of points when a little bit of modern tech works well with old school parts....I’ll keep digging

When you remove the electronic module it would be a good idea to have a good look at the wires. You may well find the problem.