Why does the engine stall when idling normally but accelerating hard?

[DeHarrison]

There are two situations when the engine idles normally but stalls when accelerating hard: 1. The first situation: The engine stalls due to an overly rich air-fuel mixture in the engine. An overly rich air-fuel mixture means excessive fuel injection in the engine. Common causes for an overly rich mixture may include a faulty oxygen sensor or inaccurate air intake measurement. In this case, the motorcycle stalls, usually due to ignition system failure or fuel system issues. 2. The second situation: The engine stalls due to an overly lean air-fuel mixture in the engine. An overly lean mixture means insufficient fuel injection in the engine. Contrary to the above situation, if the needle seat and emulsion tube fall into the fuel bowl, the needle won't be lifted as the plunger rises, thus failing to provide enough gasoline, making the mixture even leaner. This can likely result in the inability to ignite the mixture.