Why does ignition stop advancing

[ckahleer]

Why does advance stop at 3,200 rpm. It seems logical that if that if you need 25 deg of advance going 1,200 to 3,200, you should need to keep advancing all the way to red line.

 

[Kevin Werner]

Advance is so the flame front is developing good pressure after TDC. The flame front is a fastburn and not an explosion. When the piston reaches TDC the squish area adds swirl to the mixture ensuring complete (relatively) combustion. The faster the engine is spinning (piston compressing the squish area) the fasr the swirl. To much advance and the mixture is mostly burned/expanded as the piston approaches TDC. That super high pressure causes the unburnt mixture to burn all at one time, compression combustion like a diesel and hence knocking and damage. As noted on these forums, many experienced owners feel a few degrees retard from the factory spec is best.

 

[Raymond]

Another way to think about it, the advanced ignition is correct for normal running. It's slow speed running that's the special case and the ignition needs to be retarded at low engine speeds to promote smoothness when the engine is running much slower than it's best & most efficient.

 

[gggGary]

Modern systems (map) the timing using throttle position, intake vacuum, ambient and engine temperature, transmission gear selected, and other factors.
We have weights on springs. Operated by a skilled wrench/rider it compares well with modern $$$ black box motorcycles.