I also had some previous problems with my carbs and so on. I can help you a little bit on setting your float levels so that that part is fine.
Make sure that the carbs and all the jets are very good cleaned. And as you most probaly now by now that the float height is 13mm. Make sure that it's fine and set your air screw to the specs.
If you need a photo from where to where you must measure the 13mm than just ask me and I'll mail it through to you.
The carbs may be a reason why the engin is performing like that.
Good Luck