Sorry to be blunt but you're wrong on the socket size. It's a 14 mm deep well thinwall(spark plug) socket. All you need is that socket, a long extension and a ratchet and it will come right out. Done it many times already.Loosen the plugs with a regular 18mm deep socket, then take a piece of 1/4 in. id. hose about 6 in long, now grab a 3/8 in drill bit and by hand make the hole at on end large enough to fit over the new plug making a snug fit. Straiten the hose the push it on to the old plug and remove by hand install the new ones in the same manor. What is the mileage on your old plugs?
Yes I also had to modify my socket, just inserted a piece of foam rubber and it works great. I just assume they make a 14 mm spark plug socket. The reason I have removed my spark plugs several times is to see how rich or lean it's running as I am now adjusting my map. Think I have it pretty much dead on now as it's running really good.I meant 14mm socket & yes I did change plugs in my 2009 Voyager this winter at 50,000 km and they looked new. Spark plug sockets have a soft rubber insert in side to grip the plug a regular deep socket does not & at that time you could not purchase a 14mm spark plug socket here and still don't see one any where, so that is why I used a rubber hose as I mentioned previously and David if you have done this many times before your bike must have a lot of miles on it. Kawasaki only came out with this motor in 2009, have a look at how deep these plugs are in the head.
PS If any one has a 14mm spark plug socket let me know