Saving Old Seagulls

I use a 1974 40 Featherweight, which I have converted it to run on a 25:1 mixture by fitting a no 2 needle, on my 7ft dinghy. I find that to get it to run smoothly without 4-stroking I have had to screw the mixture adjustment down slightly more than 2½ turns below "flush".

Is that OK?

Even a ¼ turn less and it tends to 4-stroke when lightly loaded.

I use an TCW3 outboard oil, currenly it is Quicksilver.