You say the bike has 'sat far too long'
Did you drain the tank and carbs of all the gas before you let it set? Or did you leave the gas in as if you were going to get back to it right away?
My 1st impression is dirty carbs from gas being left in them far too long(seen this far too many times over the years)
Here is a video on setting the points and timing.
Very typical of Common Motor BS.
The #1 PROBLEM WITH THIS VIDEO is shown at 2:09 into it!With the 750 in particular, you must NEVER TURN THE CRANKSHAFT WITH THE NUT SHOWN IN THIS VIDEO. If you turn it CCW even a fraction of a rotation, you WILL bend the shaft that mounts the spark advancer. This WILL leave you with serious 'timing jitter', where the spark timing jumps back-and-forth, as seen under a timing strobe light.
The only cure is then to remove the points plate and spark advancer, re-straighten the shaft with a dial indicator to less than 0.002".
For those interested, here is the PROPER way to set points on the CB750:
1. Remove the sparkplugs.
2. Mount the points and wiring.
3. Using the kickstarter or via bumping with the electric starter, turn the engine 180 degrees past the 1-4 "T" mark. Set the 1-4 points to 0.014" gap here.
4. Using the kickstarter or via bumping with the electric starter, turn the engine 180 degrees past the 2-3 "T" mark. Set the 2-3 points to 0.014" gap here.
5. Using a strobe timing light, start the engine and find out where the 1-4 timing marks are located. Turning the baseplate adjusts this set of points: do that to make it fire on the "F" mark for the 1-4 points.
6. Repeat Step 5 for the 2-3 points, adjusting the smaller baseplate in its slots to reach the 2-3 "F" mark.
Now, this said...if your points plate is a genuine Honda TEC or older ND, TEC or Hitachi plate, it will go as described above.
If your points plate is a recent TEC plate, you may find that the slots in the 2 lower screw hole mounts must be widened to reach the timing marks, or the gap may be adjusted slightly, within the range of 0.012"-0.016", to reach the marks.
If you have a Daiichi points plate set, search these forums for "Daiichi" for my many, many other counsels on the issues with those plates.
If you have a CB500/550/400F/350F/250F: Honda realized this mistake of design and corrected the spark advancer mount situation in those later designs. In those bikes, you can simply remove the sparkplugs and then you can follow the Common Motor Collective video to your heart's content, but Honda never intended the SOHC4 points tobe set this way, ever. It was commonly done on the older Honda Twins, so many unknowing folks just thought the Mighty Four was the same. No, it isn't...
I'd give Common Motor Collective a piece of my mind, if I could spare it.
...end of rant...
