Thanks AVB, I mostly understood what you meant
I worked on it yesterday, and drilled a indent above the ball bearing plug and levered it out. Thankfully I didn't damage it as there is no mixture screw under there as you said.
The model is 12F802 3112 B1. Date code 03071756
Cleaning it out extra well a third time has resulted in the plug electrode going from white to a more brown colour. Adding a small cylindrical piece of oiled foam to the top air filter (has a snorkel) solved the problem completely - just made it run that little bit richer.
One day I will probably end up resizing the main jet.
Thanks
Tyler
