ORIGINAL: mrfx2001 You know, I just can't imagine a Fox 35C not running well. I currently have one that I bought when I was 15 years old that still runs like a scalded dog. (I'm 53 now) I have it on one of these Streak ARFs and have a problem flying it. It's so loud. Everything at the Field stops when it starts.
Between the first Fox Combat 35 in 1957, and the last in 1964, I owned several of them (but a GREAT many more 36's following that year's change in sizes). I was never a great fan of the Series 3, the one with twin needle bearings in the removable front end, and the back end it shared with the Rocket.
Unless you have a serious urge to go fast and be loud at the same time, a modern 28 will go as fast, if not faster, and is less noisy -- with or without a muffler. I have had some poor-performing Fox Combat engines (and there are ST & Nelson fans who will claim that all were that); and although I don't recall how seriously the first two model Fox Combats vibrated, fairly recently, I put a Red-headed Fox Rocket 35 on an old (part Sterling, mostly replacement wood from my balsa racks) P-51. It's a shaker like no other engine I can recall, other than the Sport 36 plain-bearing engine that Fox made between 1973 and about 1983.
[:-]