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.
#1
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.
#2
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