After watching a friend have 2 flying seasons basically wasted with the hassle and bother caused by several finicky Fox 35 engines, I seriously can't conceive what people see in these POS slag relics. Wasted flight after wasted flight. It's the perfect engine for people who like to endlessly tinker and trouble-shoot. Banish them all to sock drawer hell where they belong.
I had similar results - but, being a bit slow on the uptake, I kept at it for much longer than two flying sessions, it probably took me about a year of very regular flying, *dozens* crashes caused by engine issues, and 4 destroyed airplanes, before I got reliable runs. And I still, to this day, even with my subsequent 40 years of experience, *have absolutely no idea what caused most of the problems, or how what I did fixed it. For example, I have a project in the background that uses a Fox 35. Since I only got it to work with a Sullivan 4 ounce round tank, I saved the tank, still have it from the last flight in 1978, and if/when I finish, I will be running the same tank with no changes except having bleached it back out from dark brown to white again with hydrogen peroxide. I am afraid to even take the stopper out, that might make the magic escape.
Once I managed it, it was *remarkably stable*, I mean, remarkable even by current standards. As long as *you never touched it* - change one thing or even tighten a screw, and all bets were off. That's why it was a pretty good competition engine back in the 50's - it had at least equal performance to most of them, it lasted *forever*, and as long as you could get it working once, it was going to keep working until you did something. Even when it was working incorrectly, it would work incorrectly in *exactly the same way*, until you changed something, then it might work right, or might work wrong, but whatever it was doing, it would keep doing indefinitely.
That meant that as long as you didn't *have to* change anything you were set. It made it almost impossible to safely switch engines or make any real changes for performance reasons, because you never knew what you might get, it could do what you expected, or start flaming out at random again. If it crapped out, and you changed engines, all bets were off.
It has always been an exceptionally poor sport engine -almost anything else you can get, including a lot of its early-50s counterparts, was a lot easier to deal with. Even the lowly McCoy 35 Redhead which was a bargain-bin special, could be thrown together and work without a lot of fuss. It wore out quickly, performance was nothing to write home about, but it was probably going to work and not require a month or random experimentation to stumble on a functional system.
Now, of course, all of the vintage engines are far more difficult to deal with than the low-ball cheapest modern engines. The things these old engines have going for them are nostalgia and the fact that there are *tens of thousands* of them just lying around to use.
It makes nearly no difference to me what engines people use, but when I see someone struggling or having issues, it is rather frustrating to watch them screw around with problems that have long since been solved just because of nostalgia.
Brett