The older 23.6cc Echos had the larger ports. I believe they were made in the mid 90's.

Here's my new twin 23.6cc engine running 10 minutes ago.

Started on the third flip. Runs so smooth you can't even see the gasoline in the tank jiggle or feel any vibration at all on the test stand. It's only got 10 minutes on it, and no fine tuning, but already turns a big old 20 x 10 wide blade APC at 6500 rpms... After about 25 minutes of easy running, I shut it off, and it restarted on the second flip of the prop. Yep, I think I'm going to like this one!

I think I'm going to build another one with 25cc crankshafts, some port work..... oh boy, here we go again!

AV8TOR