Starting and Running Problem...

Well, need more info.

When you say that you tightened the valves, do you mean that you tightened the adjustable rocker arms? If so, there is a required sequence to adjusting those. With the valve cover off and the plugs removed, have someone turn the engine over and watch the rockers. Starting with the #1 cylinder, when the intake just opens...adjust the exhaust, when the exhaust closes...adjust the intake. Your intake should be adjusted to .010" and the exhaust should be .020". These numbers are for a hot engine, so you would probably be safe to adjust them to .013" and .023" cold. If that fixes it, you can recheck them hot.

When you changed the spark plugs, did you move the distributor? If so, it should be set at around 2.5 before TDC. I don't know what year model you have, but that will be very close.

Did you remove more than one plug wire at a time? If you did, you may have mixed them up.
The firing order is 1-5-3-6-2-4, clockwise around the distributor cap. The cylinders are numbered from front to rear.

On the drivers side of the firewall is a white or off-white ceramic block with some wires on it. Replace it. They are cheap and they burn up. It's called a ballast resistor.

The valve adjustment really needs to be done correctly or you could bend valves. Hopefully nothing like that has already happened.

Good Luck