Isn’t it a side-mounted problem mostly? L
Yes. Of course, queue up the "it never happens" stories, the "it's the tank" stories, and "it's supposed to do that" stories. I have seen it burp, crash, destroy the airplane, and still have the unfortunate owner come off the circle with a paper bag full of balsa raving about how great those Fox 35s run. Telling someone their Fox 35 isn't the greatest engine of all time (and would still win every contest if the judges weren't biased against it) is goring the ultimate ox. Also queue up questioning the patriotism of anyone who says otherwise - even if you won the NATs with an engine made 514 mile due south of Fort Smith.
It works unmodified *just often enough* to provide the positive reinforcement that there really isn't a problem.
Of course, there are *other* issues that can cause engines to quit, particular with a giant venturi and no compression, that explains most of the upright/inverted issues. Engines that quit unexpectedly from multiple undefined reasons are not "the greatest engine ever made".
Still, correcting the very obvious defect, as Gary did, hurts nothing and causes otherwise no problems, so, no reason not to do it and remove that as a source of problems.
Brett