How To Make a (not very efective) Throttle

This idea seems to have originated with the AE Rivers Led company of Middlesex, England, circa 1960. It was available as an "option" for their 3.5cc diesel, screwing into the crankcase backplate. The idea is to reduce the pumping capability of the engine by progressively bleeding crankcase pressure (primary compression) via a sliding plunger that slid in a flute-like tube. This would decrease the engine's ability to draw fuel and to transfer what it does draw from crankcase to cylinder. In theory, it sounds good.

David Owen decided to give it a try and made a replacement backplate for a PAW, as seen here. He reports that it had no throttling effect and was entirely unsatisfactory as a reliable cut-out. David says not having anything else but the description of the Rivers unit, he had to make an informed guess at the bleed holes, using ten 1mm holes drilled in one side only of the musical instrument, figuring he could reasonably expect some usable response. This was not the case. For the curious, the Aeromodeller description appears below.
 

Seems there are no short-cuts to the sort of throttle we are accustomed to seeing. As David says, the bottom line is that there is no easy way to throttle an engine, other than with the application of some form of barrel or butterfly to control the air supply, coupled with some facility to lean the idle mixture. Closing the air supply completely will also stop the engine, but in an unsatisfactory manner. The best and most positive way to stop is by closing off the fuel supply, or as the competition free-flight people have found, using a pressurized jet of fuel squirted down the venturi to flood the engine into inactivity. But don't let that stop you trying...