When did Fox make the change that created the Fox burp? I have a Fox 35 I think I bought new around 1961. Would it be pre burp? Just added a muffler and I am planning to use it in a Nobler.
Virtually all of them do it to one degree or another. Whether the owners recognizes or is willing to admit there is a problem is entirely another matter. Even when it quits outright and causes an inverted crash.
The one that do it least seem to have (due to the Brownian-motion quality control) the shallowest bypasses and the worst have the deepest. But it wasn't by design, it was piece-to-piece variation.
If you put it in a Nobler, you are probably fine because the issue shows up only when the acceleration is perpendicular to the cylinder axis. But does the fix takes a few minutes and either doesn't hurt, or slightly increases, the power, so no reason not to do it.