Well, you got me thinking Grumpy, I have made a few mods to the air filter, and managed to fit a nice Zama, and now she seems to be running really well.
I will need to change the throttle control cable, to suit the new carby, but that should be easy enough.
The original was a Walbro, but I cant find the numbers yet, I'll have a look tonight, under a good light.
My only thought it, will the change in carby possibly mean a change in fuel/oil mix?