Well, I figured out why it ran so inconsistently last evening - the spark plug was not tight! Doh! Well, I wanted to try a different carb anyway, to see if that was why it did not like to rev no-load. It will be a little tough to tell now as I've changed several things at once. With the spark plug in properly I can feel a definite increase in cylinder pressure at low starting speeds.
Here was the cylinder with the previous porting work - the base is cut but it doesn't show up well in the picture. I've marked the intended change in pen:
Here it is after grinding:
The cylinder is not perfect, but most of those scratches are shallow and below the port.
The timing (duration) is now:
E = 147
I = 161
T = 106
Here is the WT391 installed. It will now use the splined Husky/Poulan adjusters rather than the D screws:
It started right up with the screws as they were adjusted for the Poulan it had been in, and they only needed a little tweaking from there. It is going to get a workout today, as 2 fairly large trees fell on power lines here yesterday and I'm going over to buck up the wood. I'm cautiously optimistic as the saw feels better just playing around no load. By the way - the air filtration on this saw is excellent.
First I need to go put the 25" bar on its Chinese clone brother.