Wont run on prime setting on fuel tap

Hi,

On most Japanese bikes, the PRI position allows fuel to flow from the tank to the carbs even if the engine is not running. In the ON position, the fuel gate valve would only allow fuel to flow if there is vacuum which of course would mean that the engine is running. There is normally a vacuum hose from the intake manifold of cylinder 1 that leads back to the fuel valve that triggers the internal diaphragm to open the fuel line.

If we are to assume that for some reason the PRI position is blocked, then switching the "fuel tap" to this position would not allow fuel to go down the carbs. Thereafter, the engine used what fuel was left inside the carbs (100 meters) and the engine died. Switching the "fuel tap" back to ON again would not allow fuel to flow down from the tank to the carbs since there is no vacuum and very little vacuum when starting the bike; and the bike would not start, no fuel inside the carbs.

Correct action of course would mean overhauling the "fuel tap" and initially setting it to PRI and then to ON soon as the engine is running on its own. Temporary remedy/workaround would be to manually feed fuel to all the carbs with the use of an external container with rubber hose/fitting. Alternately, you can try spraying starter fluid or car injector cleaner. This should be done with the air cleaner off. A word of caution, in some older bikes I have worked on, this condition would result to an overflow of the carbs soon as the engine starts indicating that the float(s) inside the carbs are sticking.

Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information. Good luck and kind regards. Thank you for using FixYa.