Repairing a Lucas 25D distributor with a Bad advance curve

At a recent tuning session, this distributor was determined to be giving bad ignition timing.
Taking the unit apart revealed that someone had removed the primary spring. With only the secondary spring operating the advance curve, this car had approx 10 degrees of total ignition advance.
After cleaning, polishing, and greasing the internal parts, a new primary spring was sourced and installed. This was tested on my distributor machine to prove that the advance curve as in fact back to specifications.
Vacuum advance as well as total advance also checked.

[@georgemoore2928]

So I have one of these in my 1982 Land Rover. The Haynes manual says that the mechanical advance should go as much as 42° at 4500 rpm. But mine has the same cam in as yours with 12° stamped on it. Does that mean that I have the wrong cam? Should it say 42° on the cam? Thanks

[@darrensrestorations991]

The distributor cam is not the same as total advance. 12 deg of distributor advance is 24 degrees at the crankshaft. Add on the static idle advance and you should get to total advance. The Haynes manual may be referring to the total advance including any vacuum advance.

[@codelocust3297]

when distributor in place, can the rotor arm rotate a bit or is it wear?

[@darrensrestorations991]

If the rotor rotates but the shaft does not, that is an issue. The rotor and shaft will rotate together and swing out the weights which is normal.

[@zingzing5077]

Hi, just replaced the vacuum advance unit, and I couldn t find any info on how so set it up. How many clicks or what should I measure to find a proper set up. Thank you.

[@darrensrestorations991]

Set timing to what the book says without vacuum hooked up. Then hook up vacuum.

[@zingzing5077]

@@darrensrestorations991 Hi , iment the vacuum membrane that moves the points.

[@darrensrestorations991]

If it is a 25D distributor, set the adjuster wheel to the center or middle of the adjustment range.

[@biffick99]

Interesting about checking the advance with the protractor. I understand about the pointer but where is the stop line to read the amount of degrees to check if it concurs with what's stamped on the cam?

[@darrensrestorations991]

Rotate the rotor cam untill it stops, then read the protractor. That will be the number of degrees of advance that you have. Sometimes it matches what is stamped, but wear on the cam will lead to more timing. Which is why it must be measured.

[@biffick99]

@@darrensrestorations991 Thank you. Yes, I get it now.