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Choke Operation

While few automobiles still have chokes with the advent of fuel injection, motorcycles still are predominately carbureted, using manual chokes.  The last manual choke car I saw was a 1975 MGB.

While I will continue to refer to the carburetor starting equipment as a choke they are actually a system of richer jets that  provide the needed extra fuel to allow the starting and cold-running of  the engine.

When starting a bike cold, it works best to fully engage the choke and leave the throttle CLOSED.  Opening the throttle upsets the vacuum differential needed for the proper operation of the choke.

Once the bike starts and catches on all the cylinders, ease the choke off a bit to allow the motor to idle up.  Depending on the particular bike, you should be able to now drive away.  Ease the choke off as the bike will run without it, not forgetting to shut the choke off completely as soon as the bike no longer needs it.  The length of time needed for application of the choke will become apparent as too quickly taking off the choke will cause hesitations and too long a time with the choke on will load up the motor, generally showing itself as a misfire the first full power application that goes away shortly afterwards.  Experimenting with this rate of application will soon show how to get the best behavior characteristics of the individual bike.

Having to run the bike with the choke on to get it to run properly when fully warmed up is generally a sign of carburetor or air leak problems and should be addressed by a competent facility.

Hope this takes some of the mystery out of  cold-motor starting.

© Bill Whisenant 2007
updated 10/23/07



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