CIS 1973.5 Issue

[Jay Laifman]

I've been chasing a hard start problem. In doing so, I recently bought an AEM wideband O2 gauge. I do not have a bung, and I'm using an Innovate adapter that slides a pipe into the exhaust. I got an odd result and I'm wondering if anyone has some thoughts.

Factory spec says to set the CO% at 2.5-3%, which is 13.56-13.38:1 AFR. When I do this, the car runs poorly. It is not smooth, kind of grumble/rough. I need to richen it to make it run smooth. But t

I know the Innovate pipe adapter is not supposed to be accurate for some cars at idle. But I believe that it reads leaner than it should, which caused cars to be set too rich. That's not what is happening here.


I'm wondering if this is showing I have a leak in my airbox, creating an overly lean situation that needs more richness to compensate. I did do multiple smoke tests and didn't find anything. But maybe I missed something. And maybe that is causing my hard start problem.


I also tried the gauge on my 912 and got an equally odd result. When I move the pedal to 80%-100% WOT, the car gets much richer (10:1). Even with the accelerator pumps disabled. Trying to figure that out too. Maybe the better answer is to not bother with the gauge!!!

[Chickenstrips]

On my 1973.5 when I had hard starting problems it was always one of two things that were not the richness/lean setting: it was either CSV (not getting power, or microswitch not closing to ground), or leaky intake tubes leaning things out at near idle when vacuum . Until I rebuilt the engine with new intake tubes, and a new airbox, I didn't realize that almost instant starts were a dependable thing. On my 1974, it is 100% always the CSV - loose connector, or bad thermotime switch, which I finally bypassed.