Smoke from a muffler is generally only an issue on a machine that has been smoking/burning oil for a very long time. Especially on a 4 cycle motor. I doubt your exhaust is the source. 2 stroke motors are common for that, because they're constantly burning oil. Over the years a littlenunburnt oil turns into a lot of buildup in the muffler.
4 cycle engines are a lot cleaner because the oil doesnt (shouldn't anyway) come into direct contact with the combustion. Valve seals are possible, theyll make it smoke on a first start. And if.youre driving and let off the pedal to coast to a stop, itll blow a puff when you first start going again. But if it's smoking AS you're burning the throttle, its 99% going to be oil control rings sticking.
You can try a bottle of motor flush, pour some in, drive it around the yard lightly for about 10 minutes then immediately change the oil. If the rings are marginally stuck by sludge, it may help. But may do nothing except make your 1 day old oil you just put in look like it's never been changed before. I've loosened some NASTY stuff before. Always ended up having to rebuild the motor because by the time I got it, it was.too far gone. But cant hurt to try.
This is the stuff I have used. It's cheap, around $5 or so st Walmart. Worst case it doesnt work and you still have to tear into the engine. Niteo Motor Medic MF3 5-Minute Motor Flush - 32 oz.
https://www.amazon.com/dp/B000AME4V4..._jDTFDb4N2QTQZ