You said spark is good in your first post. Then in your reply, you said "I still think it's a weak spark". How can anyone assist in this troubleshooting?

If you have a weak spark, make sure that the complete ignition system is good (coil, distributor cap and rotor, if applicable, spark plugs & wires). If they are all good, check for battery voltage & ground at the coil. Check this at rest and while cranking (what is it dropping to?). Do you have weak spark at the plugs, but good at the coil? What is the whole situation here? How far will the spark jump?