Throttle mechanism
 

Is it mainly the peewee engine sthat use a throttle ring? Do the larger engines have a more complicated mechañism? Do throttle rings restrict the exhaust flow?

The Cox .049 and .09 also have the throttle ring. There is a Medallion that has a combo carb and sliding exhaust restricter too. There might be more. There is virtually no power loss unless it is the muffled ring. Unless it is closed of course. Some of the old engines had coupled butterfly valves on the exhaust for a better idle. That was before mufflers were fashionable.