If you have a Sunoco station there, check it, derf. That's the predominant station that sells the good stuff here. The local boat dock here is selling it for $4.35 per gallon!!!!

Thanks, guys!

In for warranty claim at Briggs and Stratton authorized service center. Should get to it this week. Dude said he smelled no gas in the oil nor did it smell burnt. Air cleaner is dry so breather likely ok and carb float probably stuck.

That leaves head gasket, cracked block, and cracked head. It is not overfilled with oil and I was emptying the bag when it went down. It only smokes after 10 seconds of running and puffs a constant reproducible amount of smokes on each firing while running quite smoothly.

My guess is head gasket just starting to fail or hairline crack in head, neither of which come into play until they begin to heat up and the surfaces separate from thermal expansion

Bones,

no eco-mods?

(Sigh)

Just when you think you know a guy he wants to hot rod your mower but ignores aerodynamics

Verdict is the following.

Slight bit of oil on the air cleaner was getting sucked into the cylinder. How did it get there? Oil slosh while mowing the edge of my property which has a hump at the property line and a bunch of deep divots that the front wheels get into and bottom out, then pop out of. It's been 5 years I've been cutting my lawn with two different mowers, 2 years with this one and this has never happened before. Guess I'll have to slow down and keep a few spare air cleaners around. Never thought to take it off to troubleshoot, but even if I had, I would have thought it was a crankcase pressure issue pushing oil into the air intake just like excessive blowby in a car engine. I've never had to troubleshoot a small engine before other than when I tipped over my pressure washer when it slipped off the table it was on while I was working on it. Not surprisingly, the cylinder filled with oil. However the air cleaner did not get any oil on it. Whatever. Also found out that when extremely hot other, stopping for too long resulted in too weak or no spark and and a no fire condition. I always assumed this was the signature of a magneto issue, but when my current mower was checked, he said the plug was the issue, not the magneto, and the plug was beginning to gas foul from the weak spark. Put them together and the thing won't run. I assume you tell the difference by putting a new plug interested in a while hot or heating the existing one with a heat gun until it fails. Same deal for the magneto.

Now on to my beloved 22 yr old craftsman weed whacker. 2 cycle. New carb, new
fuel lines new fuel filter, primer bulb failed AFTER that. Can't get the thing to idle unless it is racing and the fuel filter seems to want to float which I assume means there is air trapped in it. Also I think the gasket between the carb and the rest of the unit has a slight tear in it and is letting unmetered air in, leaning out the mixture, thus requiring more fuel per unit time which eventually fouls the plug and it stops running. Then when I check for spark there is none, even after the plug is mostly dried off.
Shall I replace the gasket and plug and go from there? The carb has no mixture adjustment. The unit has only an idle adjustment screw, so everything else needs to be in order for the thing to run properly.

Am I headed in the right direction?

Double check the gasket, derf. Sometimes it's easy to put it in backwards. And double check your new fuel lines and make sure you got them routed properly. Sounds to me like maybe you put them on in reverse order and instead of pumping gas into the carb, you're pushing air into the tank. How do I know to check that? I've done it myself. That's why I still just replace one line at a time anymore. Also, if you nicked a small hole in one of the fuel lines, it can drive you nuts. As for the mower, I've never heard of such a thing. Just keep an eye on that thing for white smoke. Sounds to me like maybe they blew some up your tail pipe!!

No, it does happen with the OHV 4 strokes these days.

I can get it to run (weed whacker) and I have already figured out the lines are not on backwards by previously putting them on backwards. The mix is just all wrong.

I'll replace the gasket and plug. Then I will have replaced everything there is related to air spark and fuel.