After fixing the air leak, I find I am able to get a steady low speed idle of 2000 RPM without the glow igniter. However, I notice that the engine hunts (speeds up slightly and slows down) when it idles. If I allow it to idle for a long time, and suddenly throttle up to high, the engine hesitates.   The hunting behaviour and hesitation goes away when I leave the glow igniter on during idle and I also find the transition from low to high is smoother. Further, I am able to go down to a comfortable 1800 RPM on idle.

I think I'll need to use an on board glow for reliability.

Other than that, I am able to go up to a steady 7300 to 7400 RPM on an 18x8 prop. I am told that is pretty good for an engine this size and that it matches the performance of commercial 26  cc gas engines.

I think I'll stop tweaking. What size plane ( wingspan, wing loading  and weight)  can such an engine pull comfortably? I am thinking about an ultra SPAD stick build for it.