[Gaz64]

Jim,

I think we'll find the belt deflection on the engine stand is some harmonics happening that video can't capture as "true to life" due to frames per second.

A bit like vehicle wheels that go backwards on TV.

Now, your carbs.

I hope some other guys on here will chime in to say what choke size they have.

If Jim gave you 42mm, then your combo of CID, compression ratio, cam profile etc, AND intended use: driving style, peak rpm etc were all deciding factors.

A tuning book of mine shows the ideal intake tract for an IR system, to have the throttle butterfly as the same size as that of the intake valve, and then the choke to be .85 of the butterfly.

Yours would be around these figures.

I would thinking about an air corrector change that will richen the top end, something like 180 as a start. Easy enough to drill them out to 1.85 about No. 73 as a test.
Then buy the correct sizes when you are happy with your testing. A misfire (poor combustion, valve float, poor spark quality etc) leaves unused oxygen, which then shows lean.
You may see that happen as the power falls away.

Gary