WHAT plug is in it?

I would check the cranking compression on all cyclinders, and get in the habit of doing that every outing.
Pull all the plugs, block the throttle open, (leave it open for the whole time, just cover with a rag in between tests).
Record the first pump, and then what it gets after say 7 pumps.
Keep this as a record, and compare every outing.

As i previously told you, this engine will most likely want MORE retard than you or anyone else would expect. Take 2* more out of it, if you have to put a colder plug in just that one hole also.
Sawed off straps are TOO MUCH timing period !! Dont forget that

Also , at the first "mis" or "bang"....lift, its not going to "clear up" so dont put more misfires through the pipes than you have to