@Calum So there are other heads apart from them two, cool I didn't now 
At least the whole top end can be ruled out now, plus ive got a spare head to play with, so not all bad. Just need to get to the bottom of this issue once and for all.
At this rate I'll have a nice stash of spares 
@NINJA I've been doing plug chops but nothing untoward has been spotted, here is the most recent, was a new plug when the new piston went in
And here is the old head with no casting on top, yet the heads dome defo isnt the restrictive head
And the new fitted
I cant see anything wrong with the plug, but feel free to chime in
It's still basically the same 
Gotta be something else....not much left really, CDI, crankcase seals or clutching at straws for an extremely worn carb?
I've never inspected the reeds and the exhaust is a bit of an unknown, so could both be causing possible issues and shouldn't be overlooked.
Got a second hand CDI winging its way to me to rule that out. I'll do that and go from there....
@Calum It had a few small nicks, but was a whole load better looking than the other. Got it from where I bought the bike, it was the best 3mb he had, got loads of the more restrictive ones though.
Sadly no snaps NINJA, I think maybe it's a slightly older head as it had 3mb and Yamaha embossed on the top of it which the other does not
Little update. After running it in a little and opening it up a bit, I wasn't particularly impressed. It felt worse than before up top. So I did mess with the squish too much I think. Luckily managed to get another 3mb head in a more normal condition for £25 and have just fitted it and compression tested it and its up, so hopefully tomorrow's ride will be an improvement.
Now I have the old head here may as well look into getting it sorted properly at some stage and swapping back later down the line.
@Calum I'd adjusted the throttle too much so when I fired it idled around 7k I think was the reason. Took it out for 15 gentle miles yesterday and all seemed well, and took to work this morning, so far so good. Just trying to be gentle and keep the revs relatively low for the meanwhile and get some miles under her belt.
Its back together and running. Not ridden yet, but let it get to temp and adjusted idle. Took about twenty kicks to start first, but now its starting first kick. Took a compression reading before I started the engine with the exhaust off
Pretty busy tomorrow, but If I get a moment Ill take it for a spin and see what is what 
I'll be keeping a close eye on things, regular compression tests and plug chops to see whats going on.
I think I've done what I wanted with the head for now. I'd say I've given it more of a polish than anything
Its far far from perfect, but also a lot better than what it was 
one of the marks is still fingernail deep, but I'm reluctant to go much further without taking it somewhere knowledgeable with two stroke machining. I'm happy enough to fit and find out for now
