if you look at your fan shroud on your radaitor there is a white sticker showing how to do this, it also has engine specs, and the loacation of the timing advance disconnect.Is this a full size blazer? first you want to find out what degree your timing is sopposed to be set, when you look at your harmonic balancer there should be a marker line going across it, take a white paint stick and highlight this so it is visable. right above your harmonic balancer is a degree meter, if this is a 89 350 timing should be at 0 degrees. Find your timing advance wire and disconect it, get a timing light and hook it on #1 cylinder, make sure vehicle is warmed up to operating temp and ac is off. Loosen of the distrubutor bolt just enough you can turn your dist. with your hand but made sure there is some tensoin so it wont move on it's own.Start your engine use your timing light point it at the degree meter, wherever your white line you marked is at that is where your timing is, if your timing isn't whithin specs then move your distruber slowly till the timing mark lines up where it sopposed to be. tighten dist. and check timing again to make sure therer was no movement, when your done plug your timing advance back up then start vehicle and check timing again, you shouldn't be able to see the white line anymore or the line should be far away from the degree markings, if your timing is still the same weather or not your timing advance wire is hooked up your timing advance is not working.
Get a manual on your car from the parts store or AUTOBOOKSONLINE.COM and acquaint yourself with the timing of the engine.