Thank you so much for taking the time to respond. I will check out the PID link you shared.
Regarding the props, they do seem to be balanced (admittedly a bit of a home made balancer) but they stop at any point I move them to.
I shall check the motor shafts in detail this evening.
The motors are mounted straight to the frame (no spacers/ adaptors etc ...). I did put a couple of washers on each bolt as the supplied bolts were very very close to the copper winding inside the motors (good job I checked), but these are on the bottom side of the frame, so shouldn't affect anything. The motors line up perfectly with the holes in the frame, sit flat, and the bolts are snug (finger tight then a bit more, maybe 1/8 turn).
However, as suggested I will check this again.
Prop mounting - here you could be onto something ...
The props come with no adaptor rings, they just fit straight on - however, I noticed that two of them were a very snug fit (need gentle wriggling to install or remove) whereas the other two were ever so slightly looser - not rattling around loose, but can be removed with no resistance compared to the other two >>> I have a few packs of these, so will sort out x4 blades that all have the snug fit and try this,
The supplied prop nuts (M5 nyloc) are quite large, as they have a flange. I bought some spares (that a friend uses with no issues) - they are also nyloc, but do not have bottom flange so are lighter and smaller - I'll give these a go as well and report back this evening.
Once again, thank you for your help and expertise, it is very much appreciated - hopefully I will be flying soon.