help with fouling plug

What he said... Get a compression gage (under $20 at any parts store) and get a compression readings with the engine hot, all plugs removed, and the throttle blocked wide open. If it's similar to the other cylinders move on to ignition - Is the wire's insulation intact completely? Any cracks or burns in it, especially the plug boot area? If the wire's in good shape (pull it off to make sure the terminals are intact and better inspect...) move on to the plug. If you clean the plug off with brake cleaner and a wire brush will it fire? If you replace it with one from a "good hole" will it fire in the new one? If it does fire in the new location, swap the wire from 5 or 7 with #8 and see if the skip follows it. If so - replace the wire set. Fuel fouled plugs can be hard to make work again, so it may be to your advantage to replace the plugs too... but diagnose with the old ones... Once you find and fix it, stick in the new ones.