I figured it was around 26 or 27* stock?
I have never measured the piston depth at points closure to determine degrees. (Note that Tecumseh gives timing specs in "inches" before top dead center)
The thing is, there is a lot of flywheel travel across the magneto while the field expands and collapses. So in reality, wouldn't the "timing" be a very loose number? Using magnetron systems, you lose the points and condenser, so again, that has to be a loooong ignition cycle.
Cam swaps make advance keys necessary- with gasoline, about 3 degrees, and alky 5? You might try sending 125ccCrazy a PM on this subject, as he really knows his stuff, especially with Briggs FH's.