this needs very carefull looking into Joe, remeber that pattern tensioner blades have to be given a "bend" on the end before they are installed, and if not, then when turning the motor by hand the bottom of the blade can "hook" onto the chain and create an "oops", and also remember that when wheeling the bike out of the garage in neutral, the wheel is driving the chain, and turning the gearbox, but not connected to the crank other than by friction/oil drag, so if a bit drops, and you then move the bike (hopefully in neutral, but maybe between other ratios accidentally) the part could become entangled,
I hope its a kink on the chain, I had that with a 630 O ring chain years ago and it caused a drumming sensation to go through the whole bike, a bit like minscule rising and falling revs, it was a long while finding that the chain, had a kink from having been laid idle in a very tight curl for many years (actually still atatched to an engine that I boght from a Spanish write off, when I used the engine I was too tight to buy a new chain, since I thought that it had loads of life left in it, (as you do)
EVERYONE PLEASE NOTE, I NO LONGER USE 630 CHAINS EVEN THOUGH I HAVE A BRAND NEW ONE STILL IN A BOX AND THREE SETS OF SPROCKETS, YES I HAVE SEEN THE LIGHT (CIBIE)
CLEM