Stuck spark plug, Have you tried to take a mirror and look down the
spark plug bore? This is a long shot,(but it happened to me).
In trying to change plugs, I couldn't get a socket on one of the inner
plugs. (The others came out very easily.) I used a small mechanics
telescoping mirror and found a small stone had wedged itself between the plug
and the wall, preventing me from slipping the socket over the nut shape of
the plug. Had to use a jewelry tweezers to grab it. Lots of fun since you
would be working in reverse (the mirror). I have no idea how it got there,
since the boot should seal the bore. Not sure if this helps. But it might be
worth a check.
By the way, I put on the Metzeler Mez4's 180 rear, 120/70 front. This
is one of the best things I've added to this bike, (besides the highway pegs
and the mirrors, and the short windscreen, and the extended bars, and the
Corbin, LOL), It does feel much lighter, easier to steer at low speed and
more agile at speed. Thanks for the tip fellow GTSer's.
Dave Schweisgut/Pa