Help! Magneti Marelli distributor issue

[AlexJ]

Hi everybody!
After a major engine rebuild, my 68 T started to run weird after 4500 rpm.
The engine struggles to increase rpm - it increases, but not as expected.
At this point, the tachometer becomes crazy and shows more rpm than in reality - it goes to 8000 rpm. This is why I relate this issue with the distributor.
It feels like at around 4500 rpm, a vibration is produced and the sparks increase frequency or the spark timing slightly delays or advance... (???).

In case anyone ever experienced this, please share your thoughts.
Thanks.

[Jerry L]

See Below, there are many threads on the Marelli distributor, the fix USED to be a Bosch as few parts were available, the issues on my 71 were not exactly as you describe, mine was wear inside the V in the advance weights So I did a Bosch several years ago.
With a engine rebuild you oue it to the engine to have a proper performing / rebuilt distributor.
PartsKlassic now has parts to rebuild the Marelli or to rebuild yours, what ever you do it needs to go on a distributor machine to see all issues, this is small $$ compared to what you just went through.

Best Regards

https://www.partsklassik.com/c-72-ignition-system.aspx

[AlexJ]

See Below, there are many threads on the Marelli distributor, the fix USED to be a Bosch as few parts were available, the issues on my 71 were not exactly as you describe, mine was wear inside the V in the advance weights So I did a Bosch several years ago.
With a engine rebuild you oue it to the engine to have a proper performing / rebuilt distributor.
PartsKlassic now has parts to rebuild the Marelli or to rebuild yours, what ever you do it needs to go on a distributor machine to see all issues, this is small $$ compared to what you just went through.

Best Regards

https://www.partsklassik.com/c-72-ignition-system.aspx

Hi Jerry,
Thanks for your outcome.
In fact I cannot change it to a Bosch because the owner wants it strictly original.

One last development because we have been testing some random solutions just trying to understand what is specifically the malfunction, was a guy working with me, decided to install a second condenser and the car runs well - apparently, stoped. At least the tacho behaves normally.
I am driving the car today to test it.

But as I don’t really like random explanations, we are trying to find out why the presence of a second condenser is having that result.
Can the first installed condenser, not being the correct one?

[bru15]

Rebuilt my 70 911. I had a couple Marellis. Sent them to a guy that does distributors and he put them on his dwell machine. Got a print out of the advance curves and he could tell me what needed fixing on them. On was a BX and one Ax...either works on the engine. Both were in dwell advance specs but one was a strait line, more wavy... said something was worn on the part where/how the weights spun out as the rpms increased. Said it would run but idle and advance rpm erratic...

[1969911T]

My Marelli is regarting randomly by about 5 degrees at idle, but fine otherwise. Maybe the your new condenser is working and the old one has opened up, which would explain why the second capacitor solved problems. You need to get a good volt ohm meter to check capacitance. I have a Fluke 87V and it is expensive, but worth its weight in gold. My original capacitor had no capacitance, but it was about 30 years old!

[66S]

Check the charging system, it can rffect ignition and tach. Bosch makes a better distributor.