Thanks everybody for the advice.

The OPS 61 is very tempting and it was only run in, has never flown.
It is a very reliable engine, starts with one swing against the prop and idles also beautifully.
On the testbench it ran a 13" prop with the same rpm's as the 11", with the 11" it just would not go higher in rpm's then with the 13"
So the prop to choose will be most probably a 11x11
The only problem is the exhaust pipe, as it hardly silences and in the Netherlands we go to max 80db at 7metres.
The exhaust connection on the cilinder is somewhat overdesigned and a normal header won't fit.
So I will need to have a header made.

Personally I like the looks of the HP61-F Gold Cup, but it has never run and I have no idea if it will perform like a pattern engine.

Also still lying around is the original Enya61X, and as far as I know that is the engine Yoshioka used with a different carburator (as the original was useless)

I also have some Webra 61 speed engines (side and rear exhaust, long and short stroke)
Looking at noiselevels the Webra 61LS with a Hatori pipe and 11x11 prop is the winner as it is very quiet

For now I will put all the engines next to each other on the table and look at the pro's and con's, and as I still have to install the engine mount all options are open.

Choises choises[sm=spinnyeyes.gif][sm=spinnyeyes.gif]

Regards,
Gert