How should the petcock actually work?

[pasteurized]

Hey all, new to the board since I picked up my 77 GS750 a couple days ago. Sweet bike, except for not wanting to start :-(. Anyway, I'm interested in how the petcock is supposed to work. On each of the settings, what is supposed to happen? I searched and couldn't find a definitive answer...

Thanks!

[Anonymous]

Prime is for priming the carbs and sometimes starting. Reserve is for reserve and you can leave it like that with the bike off, when you switch from on to reserve you get a few extra litres of fuel to get home. Run or on, whatever the last one is, is the one you usually use.

Steve

[pasteurized]

hey steve, thanks for the reply. so in any of the positions, should fuel flow all the time? i just took off the fuel line that goes out of the petcock and into the carbs (the previous owner put an in-line fuel filter in it and didnt clamp it in place correctly, so it leaked) and i got fuel all over me. i believe it was in the on position. should that have happened? in what positions do fuel flow through the petcock all the time?

[earlfor]

Prime is for filling the float bowls if they have been emptied, run out of gas, etc. Prime is a straight through gravity feed. Fuel will flow with the bike either running or not running, it makes no difference. For normal starting, you would not use the prime setting.

Run is the setting for normal use and starting. The petcock opens to allow fuel flow by vacuum pressure on its internal diaphram. You will have fuel flow only if the engine is turning over. The run setting will draw fuel down to a point where there is aprox 1 gallon remaining in the gas tank. The pick up is set high in the tank for this purpose.

Reserve is the setting that enables you to use the 1 gallon of reserve fuel in the tank. Its pickup is mounted close to the bottom of the tank. reserve is vacuum diaphram activated. Gas will only flow if the engine is turning over.

I dont believe any of the vacuum operated petcocks on GS bikes have an off selection. Usually, off is a manual/mechanical off and a valve is turned to the closed position. Gas will not flow in any condition, engine running or not.

If the bike starts to die (running out of gas) in the run position, you just switch the selector to reserve. If you are too slow and the engine uses all the fuel in the float bowls before you can get the tank switched to reserve, then you would switch to prime for about 10-15 seconds to refill the float bowls, start the bike, and then return the selector to reserve position.

Earl

hey steve, thanks for the reply. so in any of the positions, should fuel flow all the time? i just took off the fuel line that goes out of the petcock and into the carbs (the previous owner put an in-line fuel filter in it and didnt clamp it in place correctly, so it leaked) and i got fuel all over me. i believe it was in the on position. should that have happened? in what positions do fuel flow through the petcock all the time?