How are you suppose to line up the distributor cap for the timing to be perfect? The distributor cap has been a tooth off every time we try to get the timing right. The engine will start, but the idling isn't right, and extremely bumpy. It's a vortec engine. PLEASE help

When the #1 cylinder is at TDC, the rotor should point squarely to the #1 spark plug terminal inside the distributor. If it doesn't, you need to remove the distributor and rotate it a tooth (or whatever) so it does. All spark plugs should be removed first.