A lot of people on scooter motor forum made thread about "what happen with my exhaust" or i ever read "my new exhaust is not working well" i try to help the other riders and scooter motor's users to share about jetting in general. It's not an exact guideline so there's no responsibility if you want to try it.
What your modification style and purpose. Each modification with different style needs different upjets so i made some general rule to understand it more easily.
I mentioned from now, 50cc scooter and 125cc scooter is an option, bore kit or carburetor as the example.
70cc/172cc Kit: 8-12% upjet result (depend on the kit and gear, some of them need more upjet over 12%)
Exhaust equipped: 5-8% upjet result (depends on exhaust performance)
Open Filter kit: 5-10% upjet needed (depends on setup and tuning)
21mm/25mm carburetor: 4-6% upjet result (depends on setup and tuning system)
HOW TO JETTING UP CARBURETOR
How to do upgrade jetting is usual question asked by all riders and scooter motor's users. Jetting is not only about change the jet, but how to make good result and performance after jetting.
How To Jetting Guide
First of all, before jetting your scooter motor, make sure you drain the float on the carburetor until it empty. Suck the rest of draining float bowl with vacumm pipe and push until it start.
To know and check your jetting is correct, listen to the scooter motor (need practice). If it produce barrel noise so we can say it running lean. if it running with duller noise, be happy that your jetting is correct.
Another method, plug chop and run pull your bike with full throttle then as quick as you can turn off the scooter motor. Check the color of plug, white signed for lean, black sign for rich and brown is sign for good jetting.
Important Note: Check your scooter motor, some scooter and motorcycle use automatic chokes. You need to open a plug chop before you can do the test above.
So, We Start From Where?
General for jetting, scooter motor running rich is much better then running lean. Lean running will heat your engine and scooter motor or even rise up the risk of seizure on your scooter motor.
Play Diagnosis with Jetting
As i mentioned above, checking your jetting result with sound when running and the color of your scooter motor plug is not the only way. Feel the reacts of engine on different throttle level. Less power and performance produced if there's no rich running.
Most of people meet some problem when try to use percentages when share about jetting. So here the simple answer below.
Standard Jet: 60
70cc Kit Added: 12%
New Jet: 67
Use general rules as your parameter. Always consider what you doing before you change every roller on your scooter motor.
Exhaust means to drop a gram on rollers, stiffer on springs
Bigger carburetor means half a gram off rollers, stiffer on springs