What is the purpose of the fuel supply cut off on a motorcycle?

January 27, 2010 by admin · 4 Comments
Filed under: Motorcycles 
motorcycle
M asked:

What is the purpose of the fuel supply cut off on a motorcycle?
I understand on and reserve, on for the regular part of the tank, and reserve for the reserve part of the tank, but when would you (or should you) need to turn the fuel supply to off. I mean should I always turn the fuel supply to off when I park the bike? If so why? Thanks!

By the way I have a 92 Kawasaki ex500.

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Comments

4 Responses to “What is the purpose of the fuel supply cut off on a motorcycle?”
  1. Ye Olde Caveman says:
    January 30, 2010 at 9:02 pm

    The gasoline feeds to the carburetor by gravity. If the float shut off in the carburetor should happen to stick open, the gas would keep flowing. It might fill up the engine or run all over the engine and make a mess. It could leave a rider with only what is in the reserve. But if the cylinder should fill up with gas you couldn’t turn the engine over without removing the spark plug and spinning the engine to spit out the excess gas. That is a bad situation either way.
    The shut off valve can prevent all that.
    Any engine that is fed by a fuel pump shouldn’t need a shut off. The pump only runs when the engine runs. Ye Olde Caveman

  2. TeRD says:
    February 1, 2010 at 9:59 pm

    for when you have to take the tank off and have fuel in the tank, and yes you should turn it off everytime u park the bike because sometimes the gravity feed will feed your carb fuel when the bike is not in use and it will go out your over flow or it will put pressure on ur carb and thats not a good thing either for the seals and its also usefull if ur bike falls over on accident when oyur not arround so u dont lose all that expensive gas haha also if u need to take off your carb for any reason u can turn off ur gas and pull the tube off without worrying about draining your tank and making a mess TeRD

  3. We are doomed! says:
    February 4, 2010 at 10:19 am

    You probably have a vacuum operated fuel petcock shutoff on that bike. However, if it is not working properly or it is just a manually operated petcock, then the fuel would possibly leak past your needle valve in your carb and fill your cylinder with gas. We are doomed!

  4. strech says:
    February 7, 2010 at 3:25 am

    It’s to shut off the gas supply.
    As Ye Olde Caveman said, if float sticks, gas would keep flowing, not only filling engine (as Ye Olde Caveman said), but also washing oil off cylinder wall, and diluting oil in crankcase. (causing reduced lubrication).
    Figure, let’s say a petcock (shutoff) cost the factory about $5.00 (just a dollar number thrown out there). Multiply that by the number of bikes produced by that company (Kawasaki) a year. If the factory didn’t think it was needed, don’t you think they’d try to save that amount per bike per year? strech

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