So this project required some more work. I had built two ported 42cc engines, the one for this saw and a non-chrome plated older engine that went into the multi colored saw in the family picture shot above. The older engine was slightly free ported from dropping the exhaust port a little too far - but only maybe 0.015" exposed. It was more radically timed (intake duration 159, exhaust duration 164 with blowdown at 23) and ran really well.
After running a tank through each I decided to look at how the engines were doing. And both of them looked like they were scoring! Not deep, but I decided to pull the engines apart.
The old non-chrome engine had always had a shallow stripe right above the exhaust port, but it now had another forming at the side of the port - very shallow and really hard to feel. There was also carbon on the cylinder walls and piston sides, after only having been run about a tank. The chromed PP262 engine was developing two similar ones, and the piston was wearing below the intake port (but not at the bottom of the skirt). I was not happy! The rings looked great though.
So I smoothed them down with 400 grit, using a 1-3/8" dowel wrapped with some adhesively backed foam I get from work. I was able to completely remove the ones on the chromed engine, and the other is back to only the stripe it had all along. I also widened the intake port on the old engine to better match the exhaust, and I swapped out the bottom end for a much newer one.
When I put them back together I decided to swap the engines. I figured the more radical engine should have the larger carb, as the PP262 engine did not seem to be benefiting from it. I ran the one pictured in this thread (but with the other engine) quite a bit today - several tanks bucking white ash - and I have to say it ran very well. I ran the non-A/V saw a little bit too, but not so much as I didn't want to have my hands go numb. It also ran very well.
I peeked in the spark plug hole afterwards and they both look really nice - no marks or carbon, really really clean. The old aluminum engine bore looked almost new.
I'm trying to figure out what I may have done wrong. On the old aluminum bore engine I paid extra attention to deburring the ports, but if that was a problem I'm not sure how it translated into a couple of score marks. I suspect that on the chromed engine I left a burr along the lower edge of the intake port, which was binding the piston slightly and maybe causing it to dig into the exhaust side.