grumpy,

Thanks for your post - I removed the fast idle spring and engine performance improved immediately. I can now get it to idle at approx. 1500 RPM (est.) and maximum RPM appears to be about 3000 RPM (est.) - engine unloaded.
I do notice that with this engine the operating band (S - F) indicated on the remote throttle control appears quite narrow, a little above F or a little below S results in the engine staggering immediately and stopping soon after. I suppose that could be just the geometry of the cable linkage/hookup.
Incidentally, I have another query in relation to the mower itself, but I suppose that should come under another heading - so I will consider this post closed, and open a separate enquiry.

Thanks again,
mustang