Pertronix with no CDI

[Hil911]

I'm trying to track down a misfire problem with my engine. I've worked on the CIS until there seems little opportunity for improvement. For various reasons I had no faith in my original ignition (CDI, Bosch distributor), especially the coil, and decided to replace it with a Pertronix for diagnostic purposes.

SO I avoided using the CDI and existing coil. This is what I did:



The engine runs OK after setting the timing. It seems a bit angrier (which is good) and I'd swear that it's running hotter. BUT there is still a bit of a misfire and the tach is jumping a lot and possibly indicating a bit high. The tach jumps may be linked to misfires. I haven't driven it yet.

Does my wiring look OK? Any ideas for what causes the jumps? Would it be stupid to try running wires all the way from the battery?

[Hil911]

Well, I guess that silence is good! Nobody has said "Oh my God - your car is going to blow up!".

As an afterthought I plan to add a diode around where the green box is on the old points lead. I only need the current to flow in one direction: from the tach to ground through the Pertronix, so it might be a good idea to make sure that it can't go in the other direction.

[dicklague]

Why did you remove the CDI?

[Hil911]

I think that my CDI is good - it whines away happily - but I wasn't sure. I wanted to remove the entire original ignition system and go from there. I may well add the CDI back in, although I saw a note in the Pelican product catalogue that the Ignitor II is not the one to use with CDI.

[Hil911]

Hi Folks
I could really use some help with this! Since changing to the Pertronix my tach reads strangely: when I am idling the tach says 2000 RPM. Then when I get up to about 6000, it jumps back to 4000 and starts again! It worked fine before the change ... although I think the engine is running much better, probably because of the new coil.

[jbell959]

Originally Posted by Hil911

Hi Folks
I could really use some help with this! Since changing to the Pertronix my tach reads strangely: when I am idling the tach says 2000 RPM. Then when I get up to about 6000, it jumps back to 4000 and starts again! It worked fine before the change ... although I think the engine is running much better, probably because of the new coil.

Send a note to Bob Ashlock. I bet he can help you with the tach issue. He sells a tach adapt and understands the CDI and tach signals inside and out. He goes by his name here on Pelican.

[HarryD]

The reason for CDI is a hotter spark and quicker recovery time after the coil fires at higher RPMs.

For lower RPMs a Kettering ignition will work just fine as long as the coil is designed for the service.

[zelrik911]

Originally Posted by Hil911

Hi Folks
I could really use some help with this! Since changing to the Pertronix my tach reads strangely: when I am idling the tach says 2000 RPM. Then when I get up to about 6000, it jumps back to 4000 and starts again! It worked fine before the change ... although I think the engine is running much better, probably because of the new coil.

Dont worry, this is a usual occurrence when fitting a Pertronix to some german cars.
I had exactly what you describe when fitting a Pertronix ignitor to my '73 MB 450SL. (Dont think there is any connection with the misfire.)

It was recommended that I simply install an 11.5K ½ watt resister, but I never got round to it before I sold the car. I was going to buy a small tach adapt box (from Bob Ashlock ??)
There is a good description of the unit somewhere in past posts.
Peter

PS: Try some NGK Iridium plugs

[faverymi]

A while ago I follow this videos. It cleared a lot of things.

And it was a similar installation without CDI. Completely eliminated. Needed a tach adapter though...

My distributor had to be rebuilt because of the mechanical advancement. It would work well and then went completely out of time. But that is a different issue. Hope it helps



Electronic Ignition Install - 1967 Porsche 911S (Part 1 of 3) - YouTube