The ST.60 is an interesting engine. It kind of 'talks" to you and can tell you when it is propped correctly. I had a Cardinal that I bought from a local guy mainly because it had a T&L .60 in it. It weighed 72 ounces or more, but I knew if I could get a good prop it would fly a pattern. Maybe not the best pattern, but fly none the less. I just wanted to experience the ST.60 for use in some later projects.
I had learned that he usual prop of choice for the ST.60 is the 13-6 Rev-Up, but try find some of those!. The previous owner had a Zinger cut down to 12" for some reason, and would barely fly the airplane. I started to hunt around and try different props. I had read about Vess props and tried one of those one flying session. Up to that point, I had been using a Brodak 13-6 and it was the closest to doing the job, but not quite there. One flying session I had the Vess prop in hand, but put up two flights with the Brodak just to have a base line on RPM and fuel load. Next I tried the Vess 13-6. I had to start this model inverted because of the cowling and prop extension, and the guy helping me had some experience with the engine also. I started the beast up and it had the Tigre sound immediately! My friends eyes got real big and he smiled! I turned the airplane over , and in that process it broke into a two stroke for a second and went back right away. That made me get all goose bumpy! I had put in the same fuel load as before and I remember tweaking the needle just a bit for some reason, but not much. I proceeded to fly the flight with much improvement! Actual line tension up top and such. When I got to the over head eights, it broke a little more like it was running out of fuel, so I pulled out of it and after two more laps it quit, out of fuel! I had to add fuel to get the pattern in after that, that's how differently the prop was loading the engine. And as mentioned, a good, hot plug makes al the difference also. And every Fox glow plug on the face of the earth should be destroyed IMMEDIATELY!!! As it was already mentioned, I have witnessed a simple replacement of the Fox plug to be a cure for many, many engine woes!
Type at you later and have a safe Memorial Day Holiday,
Dan McEntee
PS to add, I always use an idle bar hot plug. That give jink and carbon a place to form instead of on the element. I mainly use Glow Devil R/C Longs, part number RC300, I think.