Rotor changes timing, 123 running fine, but? Options

[mgphoto]

So my engine has been really running fine except for a miss that seemed to come on at about 3200 rpms. I'm running the 123 D Jet version #B switch and no vacuum connection to the dizzy. I've pulled the timing back to 26* and I'm using regular gas with an MMT additive to control ping. This setup has been working very well as I've been testing different brands of the additive for effectiveness.
The miss I've attributed to cap, rotor and wires. I replaced the cap and rotor and before replacing the wires I took it for a spin.
The miss seemed to be gone but the ping I had tuned out was back?
I hadn't moved the dizzy, I tightened the clips holding the cap but no other change.
So I pulled the cap and took out the rotor to see what might have changed.
The new cap was identical to the one that came with the dizzy, but the rotor not so much.



I suppose that could be a 2* difference in the rotor pickups?
I put in a rev limiting 5850 rotor I had in my stash and now no miss and no ping!
If there's an issue it will find me...

[MarkV]

Okay I am game...

How exactly does the timing light know when the points open? My timing light and every other timing light I have ever seen is triggered by a lead going to a spark plug wire.... it flashes when there is energy in the wire. If the leading point of the rotor is wider then that changes the position inside the cap. The leading point inside the cap is going to send power down the plug wire sooner the light is going to flash sooner and the timing is going to be different..... probably advanced. The OP said it pinged with the new rotor so I would assume it pinged because the timing was too advanced with the new rotor.

Edit: I see where you and Dave are coming from, the electricity in the wire happens because of the points opening. The difference here is that you have changed to position of where it fires inside the cap. Think of it this way....if you were able to rotate the cap independent of the distributor you would still change the timing which is essentially what is happening here.


(IMG:style_emoticons/default/popcorn[1].gif)