Scooter problem: Smoke out of the tail pipe

Hey, I bought an old scooter and quite a bit of smoke cames out of the tail pipe. I have changed the oil. It drives fine. I think this is a very common problem, I see smoke coming from tail pipes all around taiwan.

What do you think is the most common cause of this? Sorry if is question is too broad…I know nothing about scooters.

2 stroke = normal
4 stroke = not normal, maybe the oil scrapers are busted and the thing uses (burns) a lot of oil … not good … air pollution … chance of getting a fine

If its a 2 stroke, and this just came up in another thread, then you need to give the engine a good thrashing until the smoke clears up and after that has been resolved, then you always need to ride the thing flat out otherwise the unburnt emissions emanating from the combustion chamber will build up in the cool exhaust once more and any time the exhaust finally gets up to temperature the unburned fuel within will begin to burn and release clouds of smoke once more. In short, always ride the thing flat out, which goes for any two stroke bike in Taiwan
If you have a typical 125 four stroke engine then you have some other issues. Either the mixture is wrong which should be evident by the power of the engine and the sound, as well as starting problems and idling issues, or you have a worn engine which may at best need its piston rings replaced and at worst has serious wear to valves, cylinder, piston, bearings etc.

If 4 stroke:
Dip the engine oil. Does it stink of petrol only shortly after changing the oil? Yes? Then the piston/cylinder/rings is allowing fuel and oil to mix and be burned in the combustion process. No, the oil is clean and there is little smell of fuel: Then the issue perhaps lies with the efficiency of the engine. Always best to change the oil anyway before riding it for a few days and then follow the above advice once more if it was smelly and dirty when you checked.

If the oil is fine then there may be issues with how much fuel is going unburnt in the engine and being burned in the exhaust. Check your gas emissions at a garage and adjust the carburettor to compensate, then try out the bike. It is possible that the smoke continues for some time after adjustment as there may be unburned fuel still within the exhaust that needs to be burned out by blasting the bike around until the hot exhaust has burned its innards clean. It is possible that the carburettor is at fault, in which case the garage “SHOULD” (Hey this is Taiwan) tell you anyway.

These things I have mentioned may not always be full proof advice, but may cover the vast majority of issues I see with bikes on the road.

Black smoke = bad mixture
Blue/grey smoke = oil