The stihl is not the engine to use if you are looking at that hybrid technology, the Shindaiwa C-4 is superior in the aspect of intake tract design.

Dolmar has a four stroke chainsaw. Its a 50cc fourstroke hybrid that makes .2 hp more than the 50cc 2 stroke model its eventually going to replace but the weight increase is negligible.Shindaiwa was supposed to release a version of this unit, haven't seen it yet.

and yes there are 4 stroke backpack blowers out there in the 50-80cc class that are normal 4 stroke configuration.

there is no such thing, walbro makes diaphragm carbs for small engines period. Any of the small diaphragm carbs can be set up run on any engine and no the pump spring has nothing to do with it either as Honda used carbs with and WITHOUT pump springs on the trimmers.