General Question

[bob]

What does it mean if you get a puff of white smoke. This may occurs if the engine misses slightly or if you turn if off. It is not there while running or continuous. I am asking about an older briggs 190402 from the 70's I think. I am curious about the answer as I think the problem is just old age, like me. White smoke means oil problem, correct?

[RoyM]

It is unburned fuel and nothing to worry about.

[creia]

I always thought that WHITE/LT GRAY smoke was oil related and that BLACK/DARK GRAY smoke was fuel related?
Michael

[bgsengine]

Creia has got it right. White (Technically it is gray-blue, but easy to see it as white in the usual daylight settings) is oil burning - a puff here and there is not really unusual , often indicative of your engine needing maintenance (Usually air cleaner restriction drawing oil from breather into air intake where it drips causing the puff of smoke) But if it continues or gets worse, (especially after doing a good maintenance routine) you may be seeing the beginnings of a deeper issue.

If it was BLACK/Purple smoke however, it would mean you're getting excess fuel from somewhere (Can also be caused by the same air filter needing maintenance, so it can be a faint black with white puffs every so often) Ideally, you should not even be able to see ANY of the exhaust at all, of any color.

[KE4AVB]

And considering the engine age valve guides can heavily worn. A worn intake guide or seal would show up on shutdown as vacuum is created as the throttle plate closes so oil can be draw pass a bad guide and seal. Just a worn exhaust guide can cause excessive crankcase pressure forcing oil out the breather into the carburetor which then get burned.

A good example of this is vehicle engine smoking on deceleration or as you first start revving up after a stop. Redid a lot cylinder heads when I was a teenager because of this.

[creia]

And considering the engine age valve guides can heavily worn. A worn intake guide or seal would show up on shutdown as vacuum is created as the throttle plate closes so oil can be draw pass a bad guide and seal. Just a worn exhaust guide can cause excessive crankcase pressure forcing oil out the breather into the carburetor which then get burned.

A good example of this is vehicle engine smoking on deceleration or as you first start revving up after a stop. Redid a lot cylinder heads when I was a teenager because of this.

The engines I work on and rebuild are all at least 45-50 years old. Many of them display the symptoms that KE4AVB has described and my forensics on these engines support that he is correct (no surprise!) as to what is causing the smoking.
To the OP ("Bob"): I believe that your engine is starting to show its age and extended use. Most likely not a big deal at this time if performance is still good (sounds like it is), however, it will get progressively worse with time.
Michael

[bob]

Still having problems. Compression is 100psi which I think is pretty good. My problem is that it starts good, idles reasonably well, but when I put it to work it will just die. Starts good again and may work for a while but basically dies again under load. It also is back firing while shooting out puff of white smoke. Sparkplug is quite black. I have cleaned and did valve lash. This machine has also had points replaced with solid state coil. What do you think, this is a 30+ year engine and I am thinking it ready to die

[creia]

Could be worn valve guides as previously mentioned. (You can still have good compression with worn valve guides). Have you inspected the valve guides and tried inserting the valves and doing the "wiggle test"?
Could the "spark plug quite black" you mentioned be oil fouling?
Michael

[bgsengine]

Check the flywheel key? (timing) also, may be running excessively lean (Main high speed jet not allowing enough fuel for it to stay running under load) causing misfire. Also try a new spark plug (plug may be misfiring)