1985-1986 Honda ATC250R Shop Manual, Page 63Get this manual
FUEL SYSTEM
CARBURETOR THEORY
FLOAT CHAMBER
The float valve and float maintain constant fuel level in the float chamber The float level affects the mixture throughout the entire rangeAlthough it is possible to alter the fuel mixture by changing the float level, it is not recommended
FLOAT VALVE FLOAT
STARTINGIDLE CIRCUIT
When the choke valve is opened (knob up), fuel is metered by the starter jet and is mixed with air from the primary air passage to provide rich mixture to ease startingWhen the choke valve is closed (knob down), it reduces the mixture to more normal level for idleingWith the knob down, the actual flow of fuelair is regulated by the adjustment of the chokeidle speed knobThe end of the threaded chokeidle speed knob acts as miniature throttle valve in the primary air jet passageWith the knob threaded all the way down, it cuts off all fuelair from this passage (no idle speed) and with it threaded all the way up, it allows maximum amount of fuelair through this passage (high idle speed) This circuit has two main functions; to start cold engine (knob up) or to supply enough fuel air to allow the engine to idle (knob down and adjustment properly)