I have '95 Geo Metro 1.0L, and the sticker under the hood tells me 5 degrees BTDC. There is a plug on the firewall by the left (driver's side) strut tower that needs to be jumped between the bottom left 2 terminals (top row.. blank, pin, pin, second row... pin (jump this one to next one), pin, pin), though I did not notice any change in the timing with or without the jumper wire. Hope this helps!
I have 95 Metro 3 cylinder 1.0L engine - so it is assumable, it is the same.
Under the hood is a plug (you said you found it...). The plug is covered with a rubber cover. You remove it and there should be 1 pin empty (no wire).
Turn the plug, so this "no wire" pin is at top left corner.
Then pin C and D is the bottom row - very left one, and the one next to it to the right.
I also have 95 Metro hatchback (3 door). And also, while shorting pin C and D, I do not notice any change in RPM at full engine temp (though if the engine is somewhat cooler, there is slightly noticeable difference).
My problem is, that originally when I bought it 2 years ago, I was tuning it up, and found that it runs best at about 7-8 BTDC.
It was running fairly good for over a year. But then it started to go bad on gas consumption and I tuned it up again (2x). The first time it ran O.K. at about 12-14 BTDC, and last weekend I went up to 17-18 BTDC and it runs better at low speed, but at higher speed it gets sluggish, so I think I might have to go back 1 to 2 degrees.
I have cleaned the carburetor where the injection port is, but no help.
I am getting now somewhere between 25-28 MPG average.
The car runs smooth, but the economy is gone and I do not know why...
Does anybody have any tips???