cut the end of both springs and bent the last loop 90, stiffened the system up quite a bit and was much more snappy. The RPM for full advance didn't change much if any and I still need to position the F mark for 1/4 and 2/3 to the left of the timing mark to land in the middle of the full advance zone.
Noted that before the spring mod, 2/3 were a different distance from the timing mark than 1/4 to get in the fully advance section. maybe I need to take ANOTHER loop out of the spring to make them pull harder?
If the 1-4 side reaches full advance, but the 2-3 side doesn't, I have most often found that the whole points plate itself was sitting a little bit "low" in the mounts, because the plate was slightly undersized. This happens with non-OEM timing plates, most often the Daiichi or FEW brands of plates. Raising the whole plate upward usually solves it nicely, if clumsy to do: I use some old feeler gages to shim the plate upward (in the lower mounts) while tightening the screws.
If the marks are 'jittery' or jumping around, that is due to the points shaft being bent. This favors having the 2-3 side not being able to reach full advance, too, but with the 'jumpy' timing witnessing the problem being in the points shaft and the advancer thus not being at right-angle to the points plate.
PS: the -323- advancers are for the CB350F engines, not the 750. The total advance angle is different between them.
Image of spark advancers in your book (appendix G-2) shows a K4 advancer with the 323 stamp. What am I missing?
The -323- advancers were used on a select few of the 750s during the US gasoline shortage in 1975, notably 750K4 and 750K5 bikes (that's one reason why that -323- version appears as the 3rd advancer in that picture). Their advance springs were softer than those found on the 350F, though, to achieve full advance by 2000-2200 RPM instead of 2500+ RPM, and the compression was lower in those engines as well, due to a +1mm height difference in the cylinders (and heads). Honda was advertising 50 MPG fuel economy at the time (at 55 MPH) and these were some of the 'tweaks' they used to get there. But, the top end of those bikes was about 90-92 MPH on average, so the practice disappeared quietly and quickly, and in the shop where I was then (Littleton Honda) we were issued {n} number of spark advancers to recall the bikes and change them. I only saw 1 actually get recalled and changed, but the performance difference was both immediate and noticeable.
In the 350F engines the springs are stronger and the full advance occurs nearer to 3000 RPM, but the full advance angle of the advancer is less (I think it is 3 or 5 degrees less, something like that).
To obtain similar MPG results with the stock 750 advancer we would set the idle timing at the "T" marks instead of the "F" marks, and change the float bowl levels in the carbs to the 26mm of the post-K1 era bikes. Interestingly, the bikes idled better and did get better MPG, but the upper-end performance was noticeably less. It was OK for touring, though, since you couldn't run much more than 65 MPH anyway, lest the gendarmes get pissed.
Since today it's harder to get a 'proper' advancer for these engines, I have [several times] altered the -323 advancer by grinding the notched back side of the weights at an angle (wider toward the baseplate) and then bent the 'stop' ears (and/or thinned them) to get the extra few degrees of advance angle out of them. They have a natural advantage today over the regular advancers in that slowing the spark advance curve is needed with today's gasolines because they burn so slowly compared to the 1970s fuels: with normal advancers I cut off 1-2 turns form the springs to slow the advance, but with the -323- advancer the springs seem to be just about right, provided the weights can swing further to get the same full-advance angle.
But on the whole, the -323- advancer used today in a 750 will make for a seriously sluggish performance (although the sparkplugs may stay cleaner loner).
