‘83 GS 850G petcock

[Shaftiefan850G]

Only works in prime and reserve positions. Drained tank and carbs. Removed petcock. No debris anywhere. K&S rebuild kit 55-3003 appears to be for earlier 79-80-81? 850 model. Elongated oring has 3 cross segments. Can’t tell about diaphragm part but same hole pattern. OEM petcock $72 at Babbits. Any ideas.

[bwringer]

OEM. The rebuild kits are useless junk.

The aftermarket petcocks are a mixed bag. On models where OEM is available, that's the no-brainer choice.

$72 is a little high

https://www.onlinecycleparts.com/oemparts/a/suz/50d401e5f8700230d8b4e5e0/fuel-cock

[rphillips]

Those things are really simple. Vacuum pulls on a diaphragm that pulls a plunger away from a seat allows fuel flow. Eng. off no vacuum & spring reseats plunger & stops fuel flow. If you never seen the inside of one it'd be hard to imagine how simple they are. Are you sure you don't have a leak on the vacuum line? If it's 39 yr. old it may be a possibility. The valve takes very little vacuum. You can connect a length of tubing to the small outlet on the pet cock, "gently suck on the other end of the tubing & feel the valve opening & closing. Just me, I'd look first for vacuum leak or plugged vacuum line & next take the back off the pet cock, being careful to not lose the spring, to see if I could see why it wasn't opening...What have you got to lose?

[Shaftiefan850G]

Thanks all for info. Will try vacuum pull. Vacuum and fuel hoses appear in ok shape. Will replace. Curious that Owners Manual states engine vacuum required for both ON and Reseve positions not just only ON pos. But mine only works in reserve only. Other info - Turning petcock to different positions very stiff/almost binding. Any better OEM part sources. Bike Bandit out of business??? Z1 or?

[rphillips]

Yes, should require vacuum in both ON or RES. That's what the PRI is for. If you run completely out of gas, with ON or RES. you would need to keep cranking eng long enough to make vacuum & hold valve open till carbs are full. On PRI. it just lets the fuel flow with no vacuum to fill the carbs. Same vacuum valve lets fuel flow for ON & RES., something upstream of this valve has got to be amiss. Also both ON, PRI & RES flow from & thru the same filter inside the tank. My Honda CB1100F has no PRI. if you run completely out of gas, it's a PITA to get it going again... Been there Done that.