What's up with this tank petcock?

[Guest]

Is this petcock missing something? I used a small flat head screwdriver to turn it but it just spins, so I'm not sure where it's suppose to be. Should I just replace the petcock? It must work because it was on the bike when I got it and ran fine. Top hose is for gas, bottom hose for vacuum? I've got the gas hose connected to the middle T and the vacuum connected to the 3rd carb, but I don't think the carbs are getting gas. I believe this tank is a 79 or 80, although my bike is a 78 GS1000.

[tom203]

You are a lucky guy to have the nofrills 1980 petcock! No lever to confuse you!

"Should I just replace the petcock?" Good idea even if yours seems to work, cuz it is likely 35 years old. If i recall right, screwdriver slot vertical is the "PR" spot where gas will flow once a little vacuum burps /coaxs it to life. Horizomtal would be normal "ON" where fuel only flows when engine vacuum is tugging it.
Cheap new like this Florida guy

http://www.georgefixs.com/1980-gs550-gs750-gs850-gs1000-gs1100-petcock/

[chuck hahn]

Has to be an 80 tank as the 79 and 78s had the 44 MM bolt spacing So your tank also doesnt have the indentations where then badges set..right???

And I "think" the slot up and down is the PRIme position and flat is the ON position. To PRIme the tank set the slot up and down and hit the button and crank it maybe 2 or 3 revolutions. This sucks the diapram back and it lets fuel flow. May have to repeat the hit starter button a few times till the bowls get full. That petcock works a little "differently"than whats normal.