Mark Maras

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.

Thanks, that confirms my memory. Mine were the lift type.

Going by memory it was the one in the black and white photo. Most of the 20+ years I drove it, it had a five point racing harness in it.

It's interesting that my late 70 build, 1971 Z came with the green 70 owner's manual.

My 240 was built in Nov. 70. According to the title and registration, it is a 71. The seller states that it has an Illinois title that says it's a 71. I guess he's just referring to the build year.

This isn't a "normal" vibration. Most vibrations I've encountered started above 60 mph. 30 mph is very slow in half shaft or even prop shaft speed. This one does sound like something is bent.

Taking the prop shaft to a good shop is how I (they) found a little dimple dent in another shaft that had a vibration problem.

If you don't mind sharing, I'm curious at what speed the vibration occurs? I chased a MAJOR high speed vibration (sounded and felt like 500 lb. bee trapped in the car) in my 240 that started at around 80 mph. I changed the half shaft u-joints first. Vibration was the same. New prop shaft u joints cured the vibration. The prop shaft spins 3-4 times faster that the half shafts and is more prone to vibration.

I worked for an upholsterer a long time ago. When we stitched patterns onto foam back material we glued (contact adhesive) burlap to the foam so the stitching had something to grab.

The stock air filter would be my first choice.

My options would be to drill it or use a die grinder on the rivet head.

The GM HEI is a cheap reliable option. I've not heard much negative feedback about reliability. But before you consider my opinion, know that I still like points and a condenser. I like mechanical things.

I've experienced running out of power (no miss) when the fuel filter was dirty. The only time I've experienced a high rpm miss was cured with a new set of NGK plugs.

At 5000 rpms does the engine cut out (misfiring cylinders) or just run out of power?

I can't imagine the tangs got that way accidently but I can't imagine why someone thought that would work. If my memory is correct @siteunseen has dealt with float tang angles in the past.

These forests are Bigfoot country. Yeah, they're real. Not sure what you mean by "roll down my jets" but I raised my jets (leaned it out) when I got near 7,000' with my SUs.

The clue that it happens on an incline confirms fuel starvation. Along with a fuel pressure test a fuel volume test could isolate the problem to the carbs. Have you checked the last chance fuel filter screens in the banjo bolts on top of the float covers? Post #13 you mention the front carb piston being a little sticky and a minor problem with the rear carb choke. Are those working OK now?

I've run into this problem in the past. The clutch alignment tool I used was a bit sloppy. and allowed the clutch disc to drop down a bit before I tightened it. Trans wouldn't go in that last little bit. I loosened the pressure plate just enough to be able to move the disc into the truly centered position, tightened it down and the trans slid right in.

I'd first verify the input shaft fits the bearing

I'd look into UHMW plastic for the button. It's tough, durable and abrasion resistant. Curbell Plastics sells 5' of 1/4 rod for $10.09. That small investment would build well over 200 buttons and put you in the button business.