So the smoke is coming from the top of the muffler and not from inside the muffler? Meaning the smoke isn't coming out the hole where the exhaust exits? Have you checked for oil leaks? Sometimes oil dripping on the muffler will cause it to smoke as the muffler heats up and the oil burns off. I've had that happen once. Can you post a pic of the muffler?

Thanks for replying
The smoke is coming off the top of the bracket/case holding the muffler as far as I can tell. This is the item # for the muffler:
Twin Inlet Part Number: 751-0616B
Not sure how to post the picture
Yes, I can imagine that oil is dripping onto that bracket but does that mean it is not the muffler but could be coming from the engine? And how do you tell if the muffler is bad?
Thanks again.

Thanks for replying
The smoke is coming off the top of the bracket/case holding the muffler as far as I can tell. This is the item # for the muffler:
Twin Inlet Part Number: 751-0616B
Not sure how to post the picture
Yes, I can imagine that oil is dripping onto that bracket but does that mean it is not the muffler but could be coming from the engine? And how do you tell if the muffler is bad?
Thanks again.

If the muffler is bad, your lawnmower is going to be REALLY loud. A muffler itself can not cause smoke, because all it does is muffle sound. Imagine a maze made of walls, that's what's inside a muffler. As sound bounces off each wall it gets quieter and quieter, thus muffling the sound. It does not trap engine smoke, because a healthy engine doesn't smoke.

First, I would make sure your oil cap and drain plug are tight. (You may find your problem here) Don't want water getting in there in Step 2.

Second, I would clean the entire engine area really good with some engine degreaser(local auto parts store) and high pressure water(regular hose is fine with a high pressure nozzle). Just spray it on, wait a few minutes, then rinse it off. Make sure the engine is cool before doing this. You may have to scrub any tough spots. Also avoid spraying directly at the air filter.

After that, just wait and see if you notice any fresh oil dripping on/around the muffler.

Hope this helps!

This post was edited by ENVY23 on Mon, Apr 7, 14 at 18:18

I just re-read your original post, and saw where you mentioned excess debris on the muffler. Oil is like a magnet for dust and dirt, so the debris may be sticking to the oil and hiding your problem. If you clean it like I mentioned above and let it sit, you should be able to easily identify if it is an oil leak. Good luck and keep us updated!

By looking at picture of Ryobi GAS lawn mower with Briggs engine MY guess would be the valve cover gasket leaking oil (with all that safety crap covering up the muffler and engine block). As suggested clean it off and look for the leak. IMO all old SGE's (small Gas Engines) leak oil, No big deal to me as long as the leak not bad enough for the engine to run OUT of Oil Between servicing or pouring out as fast as you pour it in.

Thanks again,
I will look for a leak in the valve but maybe more than I can handle. I thoroughly cleaned the area of ALL oil and debris before I replaced the muffler and the cover so I am pretty sure the smoking is coming from a new source of oil leakage possibly a gasket..
I think you answered the muffler question...I didn't want to replace it if the smoking was coming from another area.
Nice to know there is some help out there!