airraptor
The ZGs were as far as I know all fitted with Walbro carbs. As said, w/o a spring it rattles L/R in the venturi, but a spring holds them tight against one side. I never had to replace a carb again since I left the spring on. I don't keep track of my flying hours, but I guess after 30-40 hours they started to wear.
You are right about the prices as long as You don't buy them at modelshops or engine dealers but at chain saw service centres......

Indeed any big gasoline engine needs a kill switch that apart from the throttle can stop the engine. Some 20-25 Years ago with the first Zenoahs I lost engine control because the engine had slowly vibrated loose from its firewall (I never sealed the bolts with Locktite in those days, nobody knew then) and the displacement pulled the carb away from the servo causing full throttle.
I never forget the 20+ minutes I had to endure flying unwanted full bore with the engine sitting more and more ugly in front of the plane. After it finally died and I made a successful deadstick, it showed it was hanging just by one bolt, that was almost at the end of its threads... Nowadays with our 2-litre gas tanks on our high powered tugs, I would dislike the idea very much of having to do the same over again....
BTW: At our aerotow meets we want all tugs to demonstrate the failsafe mode on Throttle: the engine needs to go back to idle or shutdown when switching off the transmitter.