Enoch & Tatey have given good advice, perhaps buy the "Colourtune kit", this is a kit you can buy ( I think about £20) that helps set up the fueling of a carbed engine,
Don,t give up on the engine just yet, as Enoch has said ...the fact its not blueish smoke is a good sign.
Or get one of those mobile home tuners to come & service the engine
They,ll have the correct equipment & knowledge to solve your problem.
cheers
andy