Engine Break In

Proper Break-In
The goal is to let the rings wear down some to conform to the cylinder. So using 100% mineral oil, not too much, is good and then after break-in use fully synthetic oil or semi-synthetic to not smoke much and get good wear protection. These are oils that are fully mineral, without synthetic oil, and my recommended ratios of use for break-in without prolonged hi RPM runs; Dumonde Break In Oil (30:1), PJ1 Goldfire Pro (30:1), Bel-Ray SL-2 (35:1).

Good semi-synthetic oils to consider after break-in and their fuel/oil ratios for 10K-12K water cooled engines with #8 NGK plugs: Motul 510 2T (35:1), Maxima Premium 2 (not for racing. 42:1), Motul 710 2T (44:1), Maxima Castor 927 (50:1)
Full synthetic oils: Maxima Super M (50:1), Motul 800 Off Road (50:1), Bel-Ray H1-R (47:1), Silkolene Pro 2 (50:1). To read more about the details of these oils and what other oils are available just go to www.dragonfly75.com/moto/oil.html

ps - and all ratios are based upon my computer program that calculates ratios based on oil viscosity at estimated upper cylinder temp, type engine cooling, and NGK plug #. I prefer semi-synthetic oils because the non-synthetic oils have some properties that the synthetic oils don't have. Of course if you are after the most smokeless oil possible then buy one that is 100% synthetic or fully castor.

Proper break in is to help the rings wear down in conformity to the cylinder for better compression. My general suggestion is just to 1) Let it idle until engine gets hot, then let it cool down, 2) ride it easy for 15 minutes then let it cool down, 3) ride it easy but occassionally ride it WOT for short bursts, not more than 15 seconds. Those WOT bursts are when the most cylinder pressure is generated which puts maximum outward pressure on the rings so they can seat good. You can continue to use up the gas/oil mix in the tank if you don't ride hard, and then switch to a semi-synthetic or full synthetic oil at the ratios I recommend above.

Late Break In
If there is dark areas on the piston sides under the rings other than directly under the ring end gap, then there is some blowby happening due to not breaking in the rings with mineral oil. The only exception to that is when the underside of the piston is black which means oil is burning onto the underside and the sides due to excessive piston heat, usually due to lean jetting.
What To Do
Use medium grade sandpaper on the cylinder inner surface with sideways motions to create a lot of micro-ridges to be abrasive on the rings. That forces the rings to wear down at the "high spots" to conform to the cylinder and not allow blowby. Use carburetor cleaner on the piston to remove the oil burned onto its sides. Then drain the gas tank and put in fuel/oil mix using mineral oils such as Dumonde Break In Oil, Bel-Ray SL-2, PJ1 Goldfire Pro Racing. Those are the mineral oils with the highest % of group 1 mineral oil which has the lowest lubricity. Then go riding but don't ride WOT for more than 5 seconds at a time. Estimates vary as to how much break in riding is needed but I'd guess that going thru 1 gallon of the break-in mix is enough. Then go back to using a more protective oil. Oils from best to worst as far as wear protection are Castor oil, castor/synthetic blend, synthetic, synthetic/mineral oil blend, group 2 mineral oil, group 1 mineral oil.