I have a 19 IV that I bought new in the early 60's. I have flown it both in R/C with a carb, and C/L with a ventura. The threaded hole is for a baffle that was mounted and coupled to the throttle for better idle when flying R/C. A strap on muffler will work just fine, either a tube or tounge. They do take forever to break in, but they last just about forever. I have mine on a TomTom with the throttle on it for 3 line flying right now. I do use fuel with at least 25% oil, mostly castor, and 5 or 10% nitro.