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tulsawalk · 08-15-2011, 11:06 PM

MSF instructor here. I'll take a shot at clearing the mud on fuel valves:

Fuel injected motorcycle = no fuel valve

Gravity fed carburetor = On / Off / Reserve - In the on position the fuel simply gravity feeds from the tank as long as there is fuel. If you have this type of fuel system you always want to turn the valve off when the motorcycle is not running because the needle and float is the only thing keeping the fuel from flooding the carburetor, cylinders and then crank case. If the needle and float fail you have the chance of hydro locking the piston and bending a connecting rod and/or filling the crank case and diluting your oil with gasoline.

Vacuum fed system such as the GZ250 has = On / Prime / Reserve - In the on position the fuel will not free flow to the carburetor. It depends on intake vacuum to open a valve in the fuel shut off valve to allow fuel to flow. The prime position is just what it sounds like. If you bike has been parked for some time it allows fuel to free flow to the carb until the bowl fills and the bike starts. Once started the valve should be returned to the on position. You should never have to use the prime position unless the bike has sat for a time.

The reserve position is just that. It allows you a few more miles to get to a station if you run out of fuel. Of course if you forget to return the valve to the on position after filling up you no longer have the advantage of the extra fuel.

08-15-2011, 11:06 PM	#18
tulsawalk Junior Member Join Date: Aug 2011 Location: Oklahoma Posts: 6	Re: Turning off Gas MSF instructor here. I'll take a shot at clearing the mud on fuel valves: Fuel injected motorcycle = no fuel valve Gravity fed carburetor = On / Off / Reserve - In the on position the fuel simply gravity feeds from the tank as long as there is fuel. If you have this type of fuel system you always want to turn the valve off when the motorcycle is not running because the needle and float is the only thing keeping the fuel from flooding the carburetor, cylinders and then crank case. If the needle and float fail you have the chance of hydro locking the piston and bending a connecting rod and/or filling the crank case and diluting your oil with gasoline. Vacuum fed system such as the GZ250 has = On / Prime / Reserve - In the on position the fuel will not free flow to the carburetor. It depends on intake vacuum to open a valve in the fuel shut off valve to allow fuel to flow. The prime position is just what it sounds like. If you bike has been parked for some time it allows fuel to free flow to the carb until the bowl fills and the bike starts. Once started the valve should be returned to the on position. You should never have to use the prime position unless the bike has sat for a time. The reserve position is just that. It allows you a few more miles to get to a station if you run out of fuel. Of course if you forget to return the valve to the on position after filling up you no longer have the advantage of the extra fuel.
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