1982 850GZ tuning issue

[Larryr58]

Hello All, just after a bit of help on tuning the carbs on my 850GZ. I rebuilt the carbs as per the CV Carburetor Rebuild Tutorial by Ed Ness, great tutorial.
Ran the bike and adjusted the Pilot screws as per the tutorial, Carbs number 1, 3 and 4 all respond the same, screw pilot screw down, bike stumbles, screw out pilot screw 2.5 to 3 turn engine runs smooth.
Carb number 2, no matter where I position the Pilot screw, there is no affect on the running of the engine.
Cylinder number 2 spark plug black and very sooty, running extremely rich. The other plugs show some richness but no where as bad as Cylinder 2.
Any advice / help is much appreciated.

[Big T]

Your petcock diaphragm is broken and leaking fuel down the vacuum line into #2 carb. This is creating the over rich condition.
pull the vacuum line off the fuel tap, plug it and run the bike on Prime. #2 should then clear up.

Also, check that the tip of the screw is not broken off and stuck in the #2 body

[Larryr58]

Thanks for the advice, the petcock is a new replacement unit, that’s not to say there couldn’t be an issue with it, I’ll go through the process you’ve mentioned, I thought that there may be an issue with the pilot screw, l can wind it in fully closed, (seating it gently) or wind it out fully and there is no impact or change in the way the engine runs, I’ll wind it out and remove it and see if anything has broken off, thanks again for your advice Regards

[unfocused]

Also make sure your rubber plug covering the pilot jet tube is there and not by-passing.

Make sure you tune CV carbs from full throttle down to idle, not backwards.

Main jet needs to be correct first. Factory Pro has a good tutorial talking just about this.

[JDXC]

How is the hose leading from Carb 2 back to the petcock? I recently tracked down an issue I had been experiencing on my 1980 GS850G where the 2nd cylinder was always behaving strangely. Finally got it sorted when I plugged that line so I could use an auxiliary gas tank, which made me realize it had been leaking (hose was old, brittle, and didn't form a proper seal).

[rphillips]

Hey JDXC, you almost slipped in on us. Welcome. There's a place for introductions around here called GS owners, how about a little info about you and your bike. and yes, a good reminder, those vacuum hoses have got pretty old and decrepit by now, well worth a look.