What's the most overlooked issue in CIS troubleshooting?

[Beto888]

Hey all,

For those of you running CIS (especially on mid-70s 911s), what do you think is the most overlooked or commonly misdiagnosed issue?

In my experience working on these systems — especially the '75–'83 models — I've seen things like vacuum leaks, inconsistent fuel pressure, or a slightly off warm-up regulator cause major headaches, even after parts have been swapped.

Would love to hear about oddball cases or things you've learned the hard way. I’m always looking to compare notes and improve how I approach these cars.

I run a mobile mechanic service here in Utah and still see a surprising number of CIS-equipped classics on the road.
If anyone ever needs help locally, feel free to reach out or check out: here

Thanks!
BJ