I have a '91 Z28 w/ 350. Was checking everything out yesterday and found that the distributor bolt was loose and it could be turned by just touching it, so obviously my timing is jacked up. Got the timing light out, disconnected the wire to set it, no timing mark showing. Turned the dist. and still nothing. So I figured the prev. owner stabbed it 180* off or something. Set it to TDC stabbed the distr. w/ rotor pointing at #1 on the cap, put it back together and try timing again. Still not showing the timing mark. I revved it a few times and the timing mark appeared. WTF? set it turned it off reconn. the wire and started. Used the timing light to see where the mark was with the car controlling it and way off! Idle was messing up. I revved it a couple times and the timing mark moved closer to the range, let idle and was kinda jumping around. WTF do I need to do here?

 

Either the ballancer slipped (common) or the person that built the engine used the incorrect timing tab or ballancer (common). The right way to find out would be to install a pistion stop and get the engine on TDC and check where the mark is in relation to the timming tab. From here you could either try to find the correct ballancer or scribe a new mark in the old one.