The spark plug gap, on your 1994 Honda, is .013. Most spark plugs will come pre-gapped from the spark plug manufacturer.
Remove the fuel tank, Remove air box, Remove spark plug caps, Remove spark plugs ????
The usual kind of spark plugs for this motorcycle cost about $8-$10 each. You can get a discount if you buy a set of four.
12 spark plugs for a 12 cylinder engine.
pull the wire cap off, unscrew with the right size socket and replace with new sparplug, then push plug wire back on and your done.
THE INTAKE MANIFOLD MUST BE REMOVED. I WAS QUOTED > $600 TO CHANGE PLUGS. I SOLD MINE, AS IT WAS TIME FOR A TIMING BELT AS WELL. ANOTHER $600.
Use the tool that comes with the bike; i.e. in the little black pouch that's in the cavity behind the removable plastic cover on the left side. : )
If you choose NGK, then it is NGK 4929 DPR8EA Nickel Spark Plug. If you want to use other brands, then you have to look for compatible spark plugs using tables of alternative makes. Such tables can be found in the catalogs of major spark plug producers.
The Honda Shadow came with a single cylinder 125 cc engine and a V-Twin 2 cylinder 500, 600, 700, 800, & 1100cc, engine, depending on which model you buy. The single cylinder 125 cc has one spark plug. All the other V-Twin engines have 2 spark plugs.
The factory plug or OEM plug recomended by Honda is a NGK CR9EH-9. For the 1998 Honda CBR 600 F3.