I have a 1979 GS750, with the vacuum operated petcock. Has not been run for around 5 months, but couple of weeks back wheeled her out of the garage to get at another bike and put her on the sidestand. Later, noticed a pool of petrol underneath and could see a steady drip. Checked the petcock lever and it was in the run position, not prime or reserve. There had been no leak when she was sat in the garage on the centre stand all those months. Anyway, out of interest put on the centre stand and eventually the drip stopped. So when I put her back in the garage put on centre stand and no leak.
Been fine until today, when garage stunk of petrol and sure enough it was dripping from the GS again. Decided to take off tank and drain it to be safe. Usually when the tank comes off, when I dis-connect the hose no petrol comes out,but tonight it gushed out. As the tank was only about a 1/4full, found if I lifted the back end it stopped. Lowering it again and petrol came out. Got some old hose and fitted it so I could drain into a jerry can, this time when the tank lowered nothing came out !. Turned the lever to prime and it flowed, same on reserve, back to the vertical and it stopped !. Guess the petcock is screwed and needs replacing, but bit puzzled by the way it was playing up. Guess also one or more of the carbs have a float needle valve stuck open and a dodgy gasket !. Oh, the joys of old motorbikes
!!
Been fine until today, when garage stunk of petrol and sure enough it was dripping from the GS again. Decided to take off tank and drain it to be safe. Usually when the tank comes off, when I dis-connect the hose no petrol comes out,but tonight it gushed out. As the tank was only about a 1/4full, found if I lifted the back end it stopped. Lowering it again and petrol came out. Got some old hose and fitted it so I could drain into a jerry can, this time when the tank lowered nothing came out !. Turned the lever to prime and it flowed, same on reserve, back to the vertical and it stopped !. Guess the petcock is screwed and needs replacing, but bit puzzled by the way it was playing up. Guess also one or more of the carbs have a float needle valve stuck open and a dodgy gasket !. Oh, the joys of old motorbikes
!!
! Trying to decide whether to try the petcock from an old tank I have in the spares hut, or just get a re-build kit or new pattern unit. Read bad reports about both the latter. Rubber components in the old tank`s units may be shot, but may be worth a try.
