As a place to start, here's some good reading on the topic.
My own experience is also noted. Tiny turns of the little screw inside the tuna can "fixed" my idling problems, both when the engine is hot, and when cold. Sounds contradictory, but for me it works.
I've got 240,000 miles on my KF and have never done anything to it in the way of service. Nothing at all.
I do change oil & filter every 3,000 miles. That's gotta help, or at least can't hurt.
Way back in 1983 my fuel mileage dropped from 32 highway to crap. I asked a BMW dealer mechanic about it and he didn't know anything, but could only remotely guess it was "something" in the KF.
So I took the car to a shop in Huntington Beach. He removed the KF and on my instructions sent it to a (now long since closed) shop in San Pedro known to have a mechanic who understood KF's.
When I got the car back, the mpg was back up to 32 and has been ever since. Don't know what the guy did, but if something was broken he definitely fixed it right the first time.
Over in the gun world, I read about a guy, a very highly respected/guru of the Browning HiPower. I recall reading he installed a new recoil spring every 1,200 rounds, which is 24 boxes of ammo. (On some training evolutions I go through that in 6 days or less).
Is it "necessary" to change that spring when it hasn't even been broken in ?? Heck, I've still got the same recoil spring in my Colt .45 Auto after 40+ years and don't have a problem. So what does that guru know about "performance" that I am missing ?? Is he changing it just to have something to do, just because he can, because he's a "make work" kinda guy, because he's got money to burn ??
Personally, I just don't want to bother to ask why. I have my own IMHO's and performance history on that topic.
So what do I know about KF "performance" ?? Nothing really. All I know is that the KF in my '74tii has been near-perfect flawless for 240,000 miles.
I have the opposite attitude of the HiPower guy. Instead of replacing something before it breaks, I just run it till it breaks, or it seems like it's gonna break, or the car runs like crap. Then I worry about it and fix it. Otherwise, I ignore it and expect the best. I'm definitely not a make work kinda guy. And I happen to believe this stuff is a lot tougher than we give it credit for.
FINAL REPORT. Last week I removed the speedometer. There wasn't anything I could fix so I took it to Speedo Check in Whittier. Mike called me this morning to let me know repairs were complete ($95).
Just finished the reinstallation and quick road check, it is working. I'll head out tomorrow for a canyon drive and a full test drive workout.
Oh, and the cable seems to be OK. No noise at all now. I'm confident the problem was the speedometer.