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.

Help: How to install a new throttle spring on a WT-813 Walbro carb?

If you do not want to use the spring you can always take a drimmel with a cut off disc and just cut the U shape of the spring that feeds into the trottle arm off,, that way you will have no spring load at all but still have the spring in place to keep the tension on the butterfly assembly...</p>

I guess I did not make myself clear. There is no spring on the throttle at all. This is the spring between the carb body and the throttle shaft/lever. I have a new spring, and was wondering just how to put the new spring in place. Do not plan on hucking it up, just need the spring tension on shaft moving in and out.

Just wanted to add a vote for no spring. Hundreds of hours and many gas engines  have had no issues. Not saying anyone is wrong, whatever works for you. I just know what I will continue to do. And I do run a remote-cut off switch on an extra channel in all cases. But never needed it other than killing the engine normally after landing.

~Dave

John
I never succeeded in getting the spring back on. The only way would be to remove the butterfly first by Dremeling off the split screw at the bottom, then shove the axle out, but generally this is not recommended as getting the valve back in with a new screw would be difficult to secure.
Loosing that screw by vibration would mean an instantaneous demolishing of Yr engine... a new carb would be cheaper, alas.....

Thanks for the info truckracer.