You checked the gap on the #4 plug, right? Always check the gap on new plugs, even if they are "Pre-gapped." The last time I bought pregapped plugs (for my Stealth) they where set to .044". Spec is .038" to .042" for that engine.

Next, did you just unplug it to test spark, or did you remove the plug and ground the body? Or, ideally, did you connect a timing light to the wire while it was still all together?