I have a few of these, and their smaller cousin at 1.5cc, but haven't really tached it before.
With 25% castor, 33% ether and 1.5% IPN, the stock muffler and an APC 9x5 prop, I'm getting 3500rpm-10500rpm, not bad for a .12 engine.
It throttles really well and picks up from idle without any tendency for knocking.