Finally got the 1200 engine running but noticed some smokey puffs when accelerating once the engine warms up. I've done a compression test (cold) and all seems good - 140-150 psi.
The carb was overfuelling and the oil was smelling of petrol so fixed the carb and changed the oil and it still smokes. Brand new plugs are sooting up even after running for 5-10 mins.

Any ideas ?

Sounds like the valve guides are worn to me.

It is running rich so try resetting the carb the mixture screw should be approx 1.5 to 1.75 turns out from fully in if all is correct, is the choke opening fully and float level correct.

If the engine has been stood around for some time and moved now and then, you can end up with oil in the barrels which takes a time to burn out and likewise in the exhaust as well! so it might just want a good run. What colour is the smoke? blue tends to be oil, black tends to be from running rich. Worn valve guides generally causes smoke on the over-run which is blue!. Black smoke when you put your foot down is generally running rich or the accelerator pumps, pumping too much fuel in.

Rob