Offroad-Express

My 1985 surf's exhaust gase has become really fummey and becomes really apparent when engine breaking or when sitting iddling for a while considering it blows very little smoke.

Does anyone know what might be causing this and a remedy to fix it?

Any thoughts or ideas?
Cheers.

What colour is the smoke? White and you've got too much air in the mixture. Black and there's too much diesel. Then go from there