Took the CSL out for a hoon yesterday. Well I'd backed it out of the garage to spring clean, so I couldn't really put it away without running the engine warm, could I? Not sure everyone would consider that "necessary"....
With the leaky vac retard unit disconnected (and the line plugged) it ran as well as ever. Can't say I noticed any difference to the idle. Obviously the ignition timing would be the same as the unit was leaky, but I thought a plugged vac leak (only at idle per Don's info above) would have improved the idle.
Checked timing and mech advance when I got back:
Idle is 900rpm (850-950), timing at 14 btdc but a bit jumpy
At 1500 rpm timing is 17 btdc and steady
At 2000 rpm timing is steady at 20 btdc
At 2500 rpm timing is steady at 23 btdc
Perhaps the jumpy timing at idle is caused by the axial play I see in the dizzy driveshaft, due to excess lash in the dizzy drive and brass pinion. I was thinking that a slightly unstable idle would be exacerbated by play in the dizzy drive as the torque driving the dizzy would be not 100% steady. Any thoughts?