Motorcycle Repair: yz250L1 carb passing fuel, lean angles, reed valves

Question
Mark , I have a 99' yz250 that runs great. The carb has been rebuilt, new needle and float. The float height was checked with the aid of an external tube attached to the bottom bowl cap. Engine was rebuilt, new reed valves. When I run it extremely hard , gas drips from the carb vent hoses. Any ideas? Thanks, Dr. Bob

Answer
Hi Dr. Bob,

A worn needle valve and seat, varnished needle valve pin/float pin, or debris between the valve and seat are the usual causes of over-filling the float bowl and leaking vents. Exceptions are acute lean angles and inverted carburetor in which fuel may freely exit via vents.

The quad float bowl drain tube design of the FCR-MX carb prevents flooding or rich mixture when fuel level gets too high due to a number of reasons (including but not limited to rough terrain). Excess fuel in bowl just dumps out.

Unless the leaking happens with the engine off and the YZ parked, and with respect to the amount of fuel leaking, consider the leaking normal for extreme riding conditions.

Respectfully,
Mark Shively