I've a very similar setup and it sound like a bag of spanners, VERY LOUD.
I've ran the timing all over the shop and settled around the original 1.2mm, less and the idle got worse to the stage it wouldn't idle. Also it would pour white smoke.
More than 1.2 and the clack would get much worse.
I'm so concerned that I'm doing serious damage to the components, I pulled the pump last night and started to swap it back to a 9mm head.