Ran it without the muffler today after work.

IT IS IMPERATIVE THAT HEARING PROTECTION IS WORN!!!

I actually had foam plugs in as well as my shooting muffs. It was bearable.

Well, I got a little over 7K RPM with the Zinger 18X6.
Idle and transition were much better.

I did notice that when holding my hand in front of the velocity stack (blocking prop-wash), the RPMs increased and were more stable.
I rotated the angled portion of the stack to the rear. I'll have to check to see if it made a difference.

The results of this experiment are:
- The direction of the angle of the velocity stack DOES make a difference.
- The muffler is too restrictive.
- Exhaust porting will need some work.

So, maybe I'll get the porting angles and durations tonight.
I went back to the garage an hour or so later (we just can't help ourselves!) and put the timing wheel on the prop hub. Upon removing the spark plug I gazed carefully into the opening with a flashlight. The outer edge of the piston is a light gray color - not shiny but not coated with carbon. This tells me the compression is pretty good if not darn close to just right. After running without the muffler the center area of the piston cleaned up a little.

Side note: The Zama carb appears to be big enough so far. I was able to richen it to a 4-stroke cough at full throttle.

Cheers