Yesterday I created a post about an ignition problem I am having. Thank you for all those who commented. I have now run all the tests I know of and still cannot find the culprit. I have a 71 911T with Zenith Carbs and a Marelli distributor. It underwent a complete restoration in the late 90’s and recently came out of a 3.5-year hibernation. After some initial work rebuilding the carbs and getting the some the brake work done, it ran great for a few days. Then the CDI unit went bad, had it rebuilt, and again ran great until 2 days ago. After a 10 mile trip I went to restart it after lunch and it wouldn’t fire up. The engine would turn over fine. Waited 20 minutes same thing. Had it towed home and pulled off the fuel line and the pump was pushing plenty of fuel. Checked for spark and nothing.
I pulled off the distributor cap and when I toggle the advance the points are opening and closing. I also ran some fine grit sandpaper gently over them just to make sure they were clean.
I read 12 V at the center plug on the CDI with the ignition on.
I performed the telegraph test-> no spark.
I put a spark tester in the coil high tension lead and cranked the engine-> no spark
I pulled a plug wire and put the spark tester in the plug wire and cranked the engine-> no spark.
I initially thought it was the coil or the CDI unit. I recently had the CDI unit rebuilt by Bob Ashlock. He bench tested the CDI unit (including heating it up and running it hard) and the coil and they were both good. I even borrowed another good CDI unit just to make sure and still no spark.
I then checked the continuity of the wire between the C pin on the plug and the distributer and it was good. Likewise the continuity from the A pin to the coil was good. Bob also said to check the voltage at the C pin wire at its connection to the distributor. He said with the key on there should be 12 V going from the C terminal wire on the CDI to the distributor. I pulled the C wire from the distributor and put the key in the on position and no voltage at the end going to the distributor. So 12 V at the B terminal of the CDI plug but nothing at the end of the C wire.
In addition, I have cleaned, sanded, and placed dielectric gel on all the grounds and checked every connection I can see. I have included a shot of my wiring near the CDI. There are 3 loose female ends (2 coming out the same clump of wires) but I believe these have always been unconnected. The ground to the back of the CDI (bare ground) is connected to the ground in back of the plate that the CDI and other relays are mounted onto.
I know that is a lot of information but I am hoping someone can lead me down the right path.
Thanks in advance,
Jeremy
