I think the sag should be set at 1-2 inches without rider aboard. I'll have to check my manual on nitrogen charging and recommended sag. Tecates are like your quadracer, there's a valve on the reservoir. Seems like yamaha used a bladder inside the reservoir to hold nitrogen.
There's probably no way on a stock Z to adjust sag with the shock on the machine. On my 85 without the stock fuel tank, you can get to it fairly easily.
1986 Tecate
1984 Tecate
1985 Tri-Z
1986 ATC350X
1985 ATC250R (2)
1985 ATC125M (2)
1982 ATC70 - Original Owner
175 TriMoto Frame with Pro-Tec Rear Suspension
3-Wheelin' since '82