Bob:  "A good wet 2 cycle run..." From your post I understand that one can expect more of a constant speed (European?) run (2-2) rather than a more traditional 4-2-4 type run with this engine, correct? 

Robin - A year ago I spent a considerable amount of time evaluating the Aviastar .53 for John Brodak.

For initial tests, I ran it in per instructions and then machined a venturi, .30 as I recall, and installed an OS ratchet type needle valve (I prefer that style instead of the collet type). The stock muffler was nice and quiet but very heavy.

I then mounted it on the only plane I had available, a very heavy Polaris. The run was typical of a Schnuerle ported engine - too fast, lots of runaway.

As I do not have a lot of expereince with port timing but lots with head configurations, I opted for the latter. The stock configuration was a small hemispherical chamber with a large - approximately 1/8 inch squish band. Progressively narrowing the band while increasing the chamber radius eventually yielded some very nice running. The best prop was a 12-6 APC, which loaded the engine down but allowed a good wet 2-cycle run with sufficient leaning in maneuvers to keep the lines tight. When I started modifying the head, I also switched to a simple tongue muffler that I originally made for an ST 60.

The final head configuration was a .50 inch radius combustion chamber with a .04 wide squish band.
I ran muffler pressure and a non-uniflow metal tank and the runs were as consistant as I could want.
Around 5 ounces of Brodak 10/23 fuel was sufficient for the pattern.

I sent all the information back to the factory and I assume that they incorporated the changes.
I personally feel that it is a fine engine and reasonable priced.

Two things to consider:
I did no long-term evaluation so I cannot comment on the engine life.
The unit that I evaluated was a bit on the heavy side - around 2.5 ounces heavier than the ST .51.
Maybe they incorporated some weight reducing - I do not know.

Bob Z.

Hi Bob,

Have you had a chance to play with the new c/l 61 that John has on his web site? Its claimed that its not a r/c motor, its a newly developed c/l motor? Would appreciate any input, if you worked with this baby could you tell me what type of plane it will work with? (Strega, SV11, Stiletto or any other type plane that would work best with this engine.)

Thank You
  Gary