1971 911T misses after changing out CDI

[Jeremy71T]

I have a 1971 911T. Last week it cut out on me. After initially being able to start it and it cut out after a few miles, I was unable to start. I had the CDI and coil bench tested by Bob Aslock (super guy) and the CDI was bad but the coil was good. He was kind enough to loan me a CDI while he rebuilt mine. The CDI he loaned me was an upgraded version with his own electronics that is mainly used for track cars etc. I swapped it out and the car started right away but is missing and idling real low. It was running great prior to the recent issue. I can drive it but need to keep the hand throttle up to keep it going. Is it possible that the new CDI can change the timing or other ignition parameter. Any help would be great!

Jeremy

[Scott A]

I know it might be logical to suspect the one part that was changed.

But in this case I would suspect the articles the CDI touches.
So, I would be looking at the coil and points. And even the wires in-between.

Once I put a new coil in a car and it started and ran like it was brand new.

[Jeremy71T]

I know it might be logical to suspect the one part that was changed.

But in this case I would suspect the articles the CDI touches.
So, I would be looking at the coil and points. And even the wires in-between.

Once I put a new coil in a car and it started and ran like it was brand new.

Thanks Scott. Bob checked the coil and it worked fine when bench testing with a good CDI. I tried a new Brazial Bosche unit and ran the same. Makes sense that all the other things that touch the CDI could be the culprit. I will check those items. BTW, can you test timing when it is not idling well and missing?

[Jerry L]

What do your points look like? pitted ? the CDI is very easy on points in general but there is a possibility they could have been burned when the CDI was going out or died. If questionable replace them. you can set gap and an initial timing working with the distributor, set the crank pulley to an initial timing angle say 5 -10 degrees advance (not knowing build or motor) then loosen the dist clamp to allow you to turn it, move it to high spot of cam under points wear block and tighten points to proper gap. then rotate dist to points closed put a piece of a cigarette paper or other very thin material, rotate the dist towards rotor as in running turning SLOWLY and when you can just start to pull the paper out lock down the dist. timing will be close and be able to start it, then adjust timing to max advance with timing lite at say 3,500 rpm (depending on dist & build).
As to checking timing while missing or not running right, get it running right. You may play with the distributor position (timing) to see if it helps BUT mark the position before you start moving it around.

Have Fun!
EDIT:
Just noticed your screen name, do you still have the Merelli Distributor?? many have issues at idle & transition of advance as the advance weights wear down in the "corner" where they are to push the advance mechanism. I also have a 71 T but moved it to a Bosch dist. years ago this may not be the full current issue but something to keep an eye on. these parts are now available for the Merelli's where they were not years ago.
Regards

[Jeremy71T]

Thank you very much. I will take a look

[glaverbel911]

If your tachometer is going bad it can produce the same effect. Disconnect the tach wire and see what happens .