Boy the first image sure looked like it was in the wrong pivot hole but I must have been seeing something that wasn't actually there.
To me then you have a belt that is too long for your setup. I had only one case where it was necessary for me to put on a belt that was 1/2" shorter on the "F" deck. On the "G" and "H" decks the spindle pulleys can take a 5/8" (B section) but I don't think the "F" spindle pulleys are deep enough and the belt retainer covers would bind on the belt. With moving only the engagement spring your just pulling the idler around more which appears take up the surplus slack in the belt. Did you ever measured the outside circumference of the new belt to be sure someone at the factory didn't mis-labeled the belt? I know it happens as it has happen to me.
I don't know of a 1/2" (A Section) belt that would be just under the 77" since your supplier PN indicates the your new belt was 77.2". Your side of the big pond might have one but not my side. You could always try a 77" Kevlar belt. I know it is only .2" shorter but it could make all the difference as the face profile may be different. Not all belts labeled 1/2" are actually 1/2" wide.
Just thinking of possible solutions..Sometimes you just got use something that will work. Basically you got to re-engineer it at times.
