What are the reasons for a motorcycle vacuum carburetor not getting enough fuel?

[Easton]

The reasons for a motorcycle vacuum carburetor not getting enough fuel include a lean fuel mixture; poor sealing of the engine crankcase; issues with the engine reed valve, etc. Lean fuel mixture factors: A lean air-fuel mixture causes insufficient gas pressure acting on the piston after ignition, prolongs combustion time, and leads to engine overheating and other faults. Signs of a lean mixture include poor acceleration during operation. When manually adjusting the choke or pumping fuel, acceleration improves temporarily, but without enriching the mixture, acceleration weakness reappears. This indicates the motorcycle is in a lean fuel state. There are many causes of a lean mixture, mainly including: the needle valve adjusted too low; the fuel level set too low; partial blockage of the main jet; loose or leaking carburetor connections; missing air filter; or insufficient fuel supply from the tank fuel valve. Poor sealing of a two-stroke engine crankcase: Leaking or failed crankshaft oil seal on the generator side; leaking crankcase mid-seam joint; leaking joint between the crankcase and cylinder; or incorrect piston installation direction. Two-stroke engine reed valve issues: Damaged reed valve; incorrectly installed rotary valve, causing carburetor backfiring.