Another mod is the back plate and possibly the back surface of the crack case. The back place WILL need to be trimmed. See silver outline on the back plate. A common mod to the case is to take some 0.040" off the length of the case. Why? Well, with the supplied gasket between the back plate and case the inset is around 0.050" from the crank pin. I guess the thought is that by reducing the internal volume (which is compressible) the fuel/air charge will be more concentrated and more apt to provide better combustion. Just a SWAG (Scientific Wild Arse Guess).

Doing some simple measurements with both my digital and dial calipers I determined the stroke, cylinder diameter, and squish. To get the stroke I secured the head on the case with the piston installed. Turned the piston to BDC and placed a 5/16" washer over the plug hole and set the end of my calipers on the hole. I ran the depth rod of the calipers down the hole until it touched the top of the piston. The case back was still off so it was easy to visually verify BDC and TDC. I did the same with TDC and subtracted the measurements to get the stroke.
The squish was almost as easy. I took the head off and removed the piston from the case. After liberally applying synthetic 2-stroke lube, again, I gently pushed the piston all the way up into the cylinder. I took this depth measurement and subtracted it from the TDC measurement.

Cylinder dia.: 1.378", 35.0mm
Stroke: 1.129", 28.677mm
Squish: 0.038", 0.965mm

Now with some simple math, (Dia/2)^2 x Pie x Stroke, the displacement of the piston turned out to be:

Disp: 27590.5mm^3 or 27.6cc

That is about right for a 28cc engine.

The squish on the other hand should be about half of what it is. It wasn't made to be a HiPo engine so it is what I expected.

Given that the squish is large for this displacement, the exhaust appears to be restricted, and the intake is restricted, I understand better why there was so much carbon build-up inside the head. Oh yeah, the muffler. After removing it I noticed the outlet hole is quite small. Expansion muffler or no with an outlet that small (about the size of the outlet on a standard .46 glow muffler) I would also guess the engine couldn't rid itself of all the spent fuel charge. Another mod in the works...

Maybe tomorrow I'll check the combustion chamber volume and figure out what the CR (compression ratio) is. That will tell me how much I need to convince the machine shop next door to my workplace to take off the bottom of the head.

Cheers!