Quote:

If you or whomever buggered them before you didn't use JIS drivers, then what did you expect? At this point I second the needle nose vice grips.


This. At least one JIS screwdriver is necessary to keep the JIS spec screws intact. It isn't the fault of Triumph, it's the fault of the incorrect tool.
At this point I'd pull the carb bank and Dremel a slot in the screw head and see if it will cooperate. Worst case scenario the head pops off under torque but that would allow access to enough of the stem to remove.

JIS don't behave like common Phillips screws and are easily ruined by the incorrect tool, I've stripped enough over the years repairing imported band equipment to learn my lesson.

A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort. Herm Albright (1876 - 1944)