sounds like the coolant is getting in there mate has the head got any feints cracks in it or is it warped slightly at all?the smell will be the coolant burning does it smell a bit sweet?i expect it will be running weak due to the coolant being present in there which is why you are having to use the choke to give it the extra fuel it needs,i would check the level of the coolant and see if it has gone down at all if it has then it will be that for sure if it hasnt then check the gear oil level in case it is the right hand crank seal,but as a rule the coolant makes the smoke look white as it has alot of steam in in.
adam
December 2006