1985-1986 Honda ATC250R Shop Manual, Page 64Get this manual
FUEL SYSTEM MAIN CIRCUIT
As the throttle valve is raised, fuel is metered by the needle jet, jet needle, and the throttle valve cutwayThe fuel is mixed with air from the air jet and enters the venturi at the nozzle This beginning portion of the main circuit affects 18-to-34 throttleIn the 18-to-l4 throttle range, the mixture can be altered by changing the jet needle 0.0In the 14-to-34 throttle range, the mixture can be altered by adjusting the jet needle clip positionNOZZLE
JET NEEDLE
Th is final portion of the main circuit affects 12to-full throttle The mixture can be altered by changing the main jet
NOZZLE AIR JET
CARBURETOR OPERATION
The operation of the carburetor is broken into throttle opening segments; each of the metering units is responsible for one segmentThere is always overlap from one segment to the next, so any change will always affect the next segment up or downBecause of this, making carburetor adjustments for altitude or temperature should be done in methodical mannerSee page 3-29MAIN JET HOLDER