Been doing some reading and think I may have a couple of suspects. I tried leaning out the low speed needle to deal with the rich mid range and may have leaned it out too much, (even though I did the typical trick of following any adjustments with one on high speed). Apparently when you get close the adjustments can be very tight.

The other reason is perhaps the fuel inlet may have had some crap or the O-ring could have deteriorated, clogging the carb. Will have to now check the tank and blow out the carb.

Lastly, really don't know the seizing when I had it smoking quite a lot, but some of the suggestions for cowled engines means I may have more work ahead of me directing air to the cylinder. To be honest I should have run it with the systems as they would be for flight and the cowl off, rather than the complete setup, to check function before buttoning it up. Too many changes at once on a new and unfamiliar setup usually means any problems are that much harder to trace. Comfortable on new 2-stroke installs since I have so many years experience, but my first 4-stroke has proven some tricks don't carry over. Sure hope this is not the case with my others. Think the supercharged YS-91 will remain in the box till I figure all this out, since from what I read it can be one of the hardest to set up.