I'm going to bump this topic "to the top", as it is very important.
If it weren't for the stock cast pistons in the Hinckley twins, I'd say forget about the rev limiter function.
And advance curves are much over rated. All you need is retard at start-up, and all advance in by around 3000 rpms. More advance is better - till you get spark knock!
The most important input for street riding/driving (applies to cars, too) is ported vacuum advance, which I don't think these bikes have. (Ported vacuum advance allows much greater timing advance at part throttle, where combustion pressures are lower, so that spart knock is advoided.) The ported vacuum hole is located in the carb body just past the butterfly (intake valve side) and has no vacuum signal at idle. As the butterfly is opened, signal comes in, and then as the butterfly is opened farther, the vacuum drops out. This gives you greater gas mileage at part throttle, but no spark knock when you roll on the gas and go to WOT. Of course, all this can be done with sensors and electronic gizmos these days and have the same effect.
The reason the factory plays it so close to the vest on this igntion stuff is because of smog law requirements they must deal with.
There's lots more to be said on this topic, but it's almost 3:30 AM here in Geezerville and I'm hitting the hay. Retired or not, I still need my zzzzzzzzzzz's. <chuckle>
