Timing is everything

Well, that's an exaggeration, of course but I just read an old article that explained how most street bikes back in the day came with ignition set for economy rather than performance. Even more surprising was to learn that the difference in advance typically is only 3 degrees, but that those degrees really make a difference. On the Z1, the difference in timing was bigger at 6 degrees, but retarding the timing for optimum power also cost a massive 10 mpg drop in frugality!

So getting ignition timing perfect seems pretty important if you want the best possible performance from your classic.

The 550 has a 25 degree swing in timing from 10 to 35 BTDC. The tolerance alone is 3 degrees (+/- 1.5 degree).

Could it be they meant the timing tolerance, and not the actual amount of swing?

I usually set my firing mark to align with the end of the right side of the "F". They seem to like it.

My 750 twin has a total of 30 degrees advance by the mechanical advancer.

This is at full advance. Setting the timing statically doesn't mean it's correct when fully advanced. Hence you should use a strobe and check timing around 3000 rpm for best effect.