Motorcycle Repair: Carb/airbox 85 Rebel 250, stroke motorcycles, plug caps

Question
Bill,
Bike runs very poorly and dies out at full throttle with air box cover on, no filter. Fuel observed in filter and air box as though it is flooding, but nothing out of fuel overflow.   With cover off runs semi-ok but doesn't die out at full throttle. Cleaned carb, adjust per sop manual.  Plugs look black as though running rich.  Any ideas on where I should start or focus efforts.

Answer
http://www.surfmaine.com/rebel/   for some Rebel links, in general.

Louis, I don't know what kind of shape the carb was in when you started or what level of mechanical skills you have in overhauling one. The carb is fairly simple, but ou do need to look carefully at all passages, jets, emulsion tubes and check over the carb slide diaphragm for any pinholes, which will render the carb useless.

Blocked carb bowl vent passages will often eject fuel out of the carb throat, usually in a big stream, though. Running w/o the air filter will lean out the mixture a lot and the bike probably won't run well, even if everything else is fine. A certain amount of "spitback" is expected in the airbox, due to the characteristics of 4 stroke motorcycles and the pressure waves going in and out of the motor.

Check the intake manifold for any air leaks that can cause changes in manifold pressure, thus affecting carb calibration.

A sticking choke piston (starter valve) or out of adjustment choke cable will cause it to run rich all the time. Be sure that the piston is seating fully in the carb body and the cable is free to move it back and forth.

Recently a friend's 85 Rebel with 45k miles on it needed new spark plug caps as the old ones were disintegrating. The ohms readings should be around 5k ohms and both sides should be close to the same reading.

Have you checked your valve adjustments? Tight valves will cause all kinds of running issues.

Be sure that all electrical connectors related to the CDI and ignition components are all clean and tight.

Be sure your main jet didn't fall out of the holder, when you reassembled the carb! It has happened when you forget to tighten it down properly.....  

Bill Silver