Puff of blue smoke on shutdown - B&S 12hp

[ACfan]

After working the Allis B-112 awhile, upon shutdown the exhaust gives a puff of blue smoke. No smoking on startup or while running, even when pulling hard. Would worn valve guides cause the blue puff of smoke on shutdown? If not, what would?

[dirtmister16]

i would guess valve seats, but usually with them its puff at startup. it is possible, perhaps someone with more know how then i will give us both the awnser.

[D-17_Dave]

Worn valve guides or rings can lead to a little smoke puff. While running up in rpm's the heat from combustion will burn anything off and it won't be noticed. Even if the engine doesn't pass very much while running. Upon throttling down you close the carb. butterfly and this increases the intake vacuum and it may pass a little more right when you shut down. The residual heat on the exhaust valve may vaporise what small amount of oil you pass and the shutdown may push this out where it can be seen. Just my thoughts. You might try opening the throttle before shutting down so it doesn't pull as heavy a vacuum.

[HubbardRA]

Try shutting the engine down at wide open throttle. It will not pull as much vacuum and may not cause the puff of smoke. Otherwise, don't worry about it if it doesn't get worse.

[ACfan]

Thanks fellas for the response. I didn't suspect anything serious was about to happen to the engine, but wanted some reassurance. My initial guess was worn valve guides, knowing that they can be one cause of smoke at startup. But, I wasn't sure about shutdown. I'll try shutting down on full throttle to see if that makes a difference.