Once she was completed and on the road, Maggie developed a problem with a flat spot at mid throttle. The distributor was suspect, and at last I had the opportunity to tap into my collection. I pulled Maggie's distributor, and found a nonfunctional vacuum advance. Delving deeper, I found a broken spring, and the centrifugal weights quite rusty and frozen in place. After Maggie had sat up for years, this was not surprising, and in retrospect, I should have expected it.
In a quick fix mode, I popped in another distributor, the one that looked the best. It had the vacuum advance facing forward. I timed the engine by ear, and the flat spot was better, but not eradicated. Asking around, I learned that all 25D Lucas distributors are not the same. They were used on multiple vehicles, from Morris Minors to Rovers to MGB's to Triumphs. Obviously the advance curves were different, and that particular distributor advanced the timing at a higher RPM.
The easy route would have to been to order a new distributor, but I didn't save all those distributors for that! I tore three of them down and compared springs and weights to the known good distributor I pulled out of my other Rover, Beula. I combined the innards to get a mechanical advance that was similar in a housing with an aft facing vacuum canister. The 25D has two drain holes in the bottom of the housing to prevent condensation from forming. Make sure they are open.
Don't ask which weights or parts numbers I used, I don't know. I just tried to match them to my known good distributor. I put in the points using my bulletproof method, reinstalled the distributor and timed it by ear. With a functional centrifugal and vacuum advance, Maggie ran better than ever. Now, back to the rebuild!
