1980 gs 1000 fuel petcock has two connections where do they go?

Does it run ok with the petcock in the Prime position? (Pointing backward)

!980 gS750l HAS A SCREW HEAD TYPE PETCOCK. IT LOOKS LIKE THE LEVEL IS MISSING BUT THAT IS THE STOCK PIECE. TWO SCREWS HOLD THE PETCOCK TO THE TANK. REMOVE THOSE AND THE PETCOCK BASICALLY FALLS OFF. YOUR NEW ONE SHOUILD HAVE AT LEAST THE SAME BASE WITH THE SAME DISTANCE BETWEEN THE SCREW HOLES.

there is a small port on top of the second carb on the right, that goes to the small port on the fuel petcock mounted to the tank. The main fuel supply (larger port on tank) goes to the bottom fuel supply rail with the only carb port on that rail. The upper two ports between #1 & #2 carb and between #3 & #4 carbs are vents and those hoses get plumbed down under the air cleaner, careful not to pinch the vent hoses or the bowls will not fill up with gas. This is the same for an automatic petcock or a manual one.

Your petcock needs to be rebuilt (if parts available), or replaced, if it does not shut off the fuel. It also may not be saving reserve fuel , if gas is bypassing the ON position. You may also need a new fuel filter .Maybe add an additional in line filter. If you have replaced the float needles and the carbs are still overflowing you probably have a problem with rust in the tank. Have the inside of the tank cleaned or use a rust removal kit on the tank and see if this does not solve the problem. Try to avoid fuel tank liners if possible , they can cause more problems than they solve.

The best I can offer is a 1980 GS1000. Ninety eight percent of the 1980 manual applies to your 1978 bike. The biggest differences are in fenders, gas tank, decals, trim and seat designs. Go to the site below for a free download. www.carlsalter.com/motorcycle-manuals.asp

Fuel taps or petcocks can be purchased second-hand extremely cheaply from motorcycle wreckers, dismantlers or salvage yards.

Either take your old one with you or take an aluminium foil impression from the tank petcock mounting area. (bolt spacing and o-ring size etc.)

Ask for same or similar model at first to guage availability. Just be aware of the height difference between fuel on and reserve inlet stems.

Cheers.

You need to go thru the carb.s again. Looking closely for very small holes in any of the jets. Next will be to sync the carb.s together.

4 small tubes from the bottom of the float bowls, are drain hoses and should be routed between the rear of the engine and the frame.
the 4 small upper hoses are vapor relief hoses and should be routed under the airbox.
The final larger hose or hoses depending on tank are fuel inlet hoses and will connect to the fuel petcock on the Gas Tank