Fixed timing set ups need 18 to 21 degrees BTDC if you want to go fast & last.
A CDI set up 23 to 27 deg MAX BTDC at 2000 RPM,s .
But the CDI needs to retards to 15 to 19 deg,s at 6,000 to 8,000 rpm,s depending on setup port timing / pipe compression / carb / reeds or no reeds / EX back presser /weather spark plug heat rang / etc.
I think two of the big point’s that need to be looked in to or timing and compression or as my dad wood say hot and hotter.
Timing the stock timing is at like 23 to 26 deg BTDC.
It kind of works like this The carb is a flame thrower .
The more time you give the flame it the hotter things get like cylinder piston & head .
We have no vacuum advance to adjust timing with or BIG flame throwers giving less flame/heat timing at WOT but some have CDI.
So in part we need to set or timing for WOT .
Timing needs be more retarded for more top end over 6500 RPM's and more advanced for more low end power .
And the higher the performance of the motor over stock.
The more retarded from stock you want your timing !
So by reducing flame burn time in the combustion chamber we reduce BTU / heat transfer to cylinder piston & head.
Thar or three ways to do this.
The biggest is spark timing try like 18deg’s BTDC.
Next wood be a Ex system with to much back presser.
last exhaust port timing give it more timing up it 5 or 10 deg’s.
And the port is dumping more flame / heat in to the Ex system.
The exhaust chamber loves it hot up to 800 deg's f Max 4" down from flang on out side of header pipe.
As RPM’s go UP and UP it gets hotter and hotter
As it gets hotter presser goes up .
More heat and presser make the shock waves move faster moving the power band up in RPM’s at the same time = more power.
The higher the compression makes all hotter .
Higher compression makes things burn faster to (so you need a colder spark plug ).
Giving faster heat /BTU transfer to cylinder piston & head.
Compression you don’t need HI Compression with a well tuned EX system ports and carb.
A good EX system will supercharge/raise compression by over stuffing the combustion chamber.
10 or even 9 to 1 shod be fine.
Fast Bat out