I took a video in which you can hear the "whoosh" noise on throttling back - probably more of a "floof floof floof" now I hear it again. As an experiment i gave it some juice out of gear (on video) and it still makes the noise.
Actually I'm guessing, but could it perhaps be a sign of rich carb?
I can't quite hear the buzz on engine load, it might be missing from the video or my hearing.
Let's hope this works...
https://share.vidyard.com/watch/cC1dygJfFm3DwsNs2wq9HT?
The starting issue wasn't poor earth connection on the battery. Yesterday it started fine going from work, parked in the garage and started fine once more. Drove around a bit, stopped at some shops and wouldn't start. I've installed some new battery clamps from the shops. My next course of action is to call Minisport and tell them, they sold the solenoid... they might be able to point me in the right direction.