Gasoline goes bad with time and begins in as little as 3-4 weeks. This effect is known as varnishing. Jets and passageways within carbs become obstructed when varnishing occurs.
1.) Battery Test (ignition off): Meter Scale: 20V DC, Meter Connections: Red test lead to Positive battery terminal, Black test lead to Negative battery terminal, Specifications: 12V min. No more than 1V drop, If up to spec proceed; if below spec, replace battery and retest.
Most carburetor problems seem to come after the motorcycle was stored or not started for a while. If it won't start or only runs with the choke lever pulled out, you have one or more jets obstructed by gummed or varnished fuel. Notice the enrichening lever...most of the motorcycle carbs have enrichening passages inside the carburetor that WHEN THE THROTTLE IS CLOSED, provide the rich air/fuel mixture to start the engine. If you open the throttle any at all it cuts this enrichening out of the system. So if you are having trouble starting and everything looks ok, see if closing the throttle helps. This does not apply to carbs with a butterfly choke.
The elements of internal combustion engines are: correct fuel/air ratio, spark at right time, adequate cylinder compression. There are many passageways and openings to check and clean. All are important in function and when obstructed or not working properly, have subtle to radical effects on engine performance. Vacuum leaks and carburetor synchronization also effect performance and should be inspected and adjusted following the below procedures.