Mark Maras

Factory option, or dealer installed?

I've not seen one before. It reminds of that saying "Just because you can, doesn't mean you should".

Is it possible the switch is screwed in too far? My first thought is wrapping the threads in PTFE tape to encourage sealing and prevent the switch from screwing in quite as deep.

Is the "micro crack" in the dist. cap near #1?

Pull the transmission and stick your head up in the tunnel and look thru the p. plate to the clutch splines. The clutch splines should look centered in the p. plate fingers. If it's not centered, loosen the p. plate just enough to slide the disc to the centered position tighten it down and install the trans. I've successfully installed two clutches with no pilot shaft to center the disc. Honestly, on the first install, I doubted whether I could do it by eye but to my surprise, it slid right in. Same with the second.

I don't have an answer but my first impression is it's not electrical. Seems more like the throttle butterfly is opening and closing to produce that amount of variation in the rpms. It appeared that you were holding the throttle steady.

Have you tried putting the car on jackstands, starting it up, and putting it in gear to see if you can locate the noise while it's up in the air?

You say it doesn't change with RPMs but does under load. Does it change with speed?

Take a look at the one star reviews for that item at H.F. They describe the same problems with the unit.

The difference in the injected and carb grinds could be the lobe separation angle. A narrow angle between the lobes contributes to valve overlap. The closer the angle the more it kills vacuum. (Thanks "Engine Masters").

I once found a frayed (near the center) cable that was causing a speedo fluctuation.

I'm glad the issue is fixed but I'm stuck with the question, why didn't the bad u-joint show up when they balanced it previously?

Any detectable movement in a u-joint is bad and will be felt.

Was the crankshaft debacle a recall of some but not all 240 crankshafts? I had always assumed that they replaced all of them but perhaps it was only after a failure. Circa 1973 I went to the Nissan headquarters In Beaverton, Oregon with a friend who worked there. One of my memories was a surprisingly large pile (accurate description) of six cylinder crankshafts laying (thrown) in the corner. I asked about the sloppy storage of the crankshafts and he told me about the balance problem back then.

I'm beginning to think they changed belts mid year in 71 along with a number of other things.