I have used Rislone engine cleaner for decades. It does a fantastic job of cleaning additives/Varnish/Carbon and oxidation inside the crank case!
I bought a 650 out of a barn that was dirt cheap, the owner swore it was superb "when parked"
I bought it and spent the next week cleaning it up, changing fluids, new battery etc.
The day I decided to crank it over, I shot a little oil in each cylinder and kicked it over for a couple minutes before priming it and installing new plugs.
She popped off and smoked like crazy for a minute... then another minute... then another.
The fact is it didn't STOP Smoking. It still ran fine but sucked a quart of oil about every 60 miles!!! The clutch would also slip when I got on it. I'm not kidding, the City should have PAID me for Skeeter control!
I called the seller back and asked what kind of oil he used? He said regular car oil 10-w40. OH GOODY! My Brother in Law swore by Rislone so I figured I had nothing to loose. I mixed up one quart of Rislone, and 1/2 Quart of NO2 Diesel fuel,and 1/2 Qt
Castrol 20W50 changed oil with that mixture.
I rode it easy with a couple buddies in their pickup following me. It smoked worse for the first 100 Miles, I had a 2 gallon gas can with the Rislone mixture in it.
Believe me I needed it!
After 200 miles the clutch stopped slipping. after another 150 miles it was like a light switch flipped off and it stopped smoking, as a matter of fact it totally quit using oil!!!
I used Heavy Diesel oil from then on. I sold the bike at close at 40K. It still ran good but was just starting to use a bit of oil again, 1/2 quart between changes, most of it the last
700 miles.
I am thinking it was an oil control ring that was stuck. Even at that a quart to 1500 miles is virtually nothing, many bikes leak more than that! (oops 3500 thinking about my car)
I still flush my engine with either that or (Seafoam/Diesel mix) before storing for the Winter. BTW I have no involvement with any of these companies.. Just a very satisfied customer.