With all due respect to Mr. Leaddriver, - Without A/F ratio and exhaust equipment available or a dynamometer you have two means available to jet any motorcycle. You have both your seat of the pants and spark plug readings. While I do agree that modern fuel [ pump gas] makes it tougher due to variances in fuels between stations and additives you still can use the spark plug as a good measure of what is going on inside the engine. What you will be trying to achieve is the following : These are based on the 4 stroke engine.
Clean crisp starting
Quickly being able to close enrichment / choke at above 50F OAT.
Nice idle at operating temperature
No evidence of overheating quickly
Smooth acceleration from off-idle throughout the entire acceleration to top RPM.
No popping on deceleration.
No surging at steady throttle
No flat spots when throttle is backed off and quickly returned to acceleration.
The spark plug should have a uniform tan or slightly dark tone with modern pump fuels.
Deposits are usually a result of additives and or burning oil.
The exhaust pipe / muffler end can also be a sign of the engines burn characteristics.
Be aware that items not covered here are air flow through your intake and carburetor that can produce all kinds of problems. If you have a OEM air box and no modifications from the inside of the filter and on this should not be a problem. I have seen many things disturb air flow causing many issues with jetting.
Having an understand of what is going on inside the carburetor and the areas each circuit is in control of is required if you really want to be able to adjust jets to get that perfect balance of air, fuel and burning of the combination.
There are many guides out there than can give you information and help the understanding. Some motorcycle manuals even have pretty good descriptive diagrams of each circuit and what influences them.
I have been jetting motorbikes for many, many years and truly enjoy it – I know it’s weird.
Hope that helps at little.