I think the best bet would be to pull the motor and see what the rings, piston, and cylinder walls look like. If they are worn/damaged (which they most likely are from no air filter) then you could short block the motor.

Ebay has short blocks for these motors for not too much $$.

 

When you changed the oil, did you tilt the mower or drain it from below?
I've had problems with mowers smoking after tilting them to drain oil or sharpen the blade. I realize that both are cheesy shortcuts, but they do work in a pinch. It can take a while for the oil to burn off after tilting the mower for any prolonged time. I hope for your sake that it is something this simple, but considering it is recurring, you may not be so lucky. I would run it several more times to see if you can get it to all burn off. Also make sure you haven't overfilled the oil reservoir. If you did tilt the mower, let it sit for a long time before checking the oil level so that all of the oil has a chance to settle.

 

When you changed the oil, did you tilt the mower or drain it from below?
I've had problems with mowers smoking after tilting them to drain oil or sharpen the blade. I realize that both are cheesy shortcuts, but they do work in a pinch. It can take a while for the oil to burn off after tilting the mower for any prolonged time. I hope for your sake that it is something this simple, but considering it is recurring, you may not be so lucky. I would run it several more times to see if you can get it to all burn off. Also make sure you haven't overfilled the oil reservoir. If you did tilt the mower, let it sit for a long time before checking the oil level so that all of the oil has a chance to settle.

I dont think honda motors have a drain plug on the bottom...

 

They don't. At least new ones.

Gotta tip it to drain oil out the dipstick.
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My 25 year old Masters will puff a few seconds of white smoke unless the oil level is slightly below the full mark.
Check the oil level for overfull.
Also, you might smell the oil for gas.

 

Thank you all for the very helpful replies.

The mower was smoking when the oil level was not quite full, but afterwards I added enough to bring it up to the full line and it still was smoking.

I am going to take a look at it tomorrow and see if I had maybe overfilled it by accident. I will also check the oil for gas.

I don't have a lot of knowledge on the proper installation and repair of engine internals (I do this on the side, and usually only deal with smaller issues), so tearing the engine apart is a little much for me (hope to be able to get to that point in the future).

-Joe
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