The only Fox engine of mine, out of maybe three dozen the past 55 years or so, that ever "burped" some was a newish 35 stunt (newer than most of my pre-1970 oldies, anyway).  The 3-bolt 19 and its 25 size sibling not only never burped (and I've had quite a few of those, at least three of each, probably more, when they were still being made), they offered better power to weight than the 29 and 35 did.  The old 35s didn't burp unless matched to a bad tank, and the 19 and the 25 definitely quality as old.  Fox stopped making those before 1970 (the 25 was out of production before 1965). 

I think you have a bad tank.  Classic style 4-2-4 engines do not like a great many "profile" tank designs that newer engines run fine with (including OS Max-S 35s, Max-H 40s, and Johnson "S" engines, to name another trio).

OK I've got a super clown and I put a old fox 19 on it. To get right to it, there is plenty of power but a REAL bad fox burp and it doesn't like being inverted (moving the tank was no help). I haven't torn into it yet but I'm thinking of filling up part of the intake port.
Any suggestions will be helpful.

Is it the 3 bold, the 4 bolt or the newer one? 

Bill,

I'll presume your Fox 19 is the 4-bolt backplate, bolt-on venturii type?

This one likes to rev, and does so very happily. At good RPM, it draws fuel well. If your prop is too much load, it might not get 'on its step.'

(Reason for my guess: The old 3-bolt backplate Fox 19s are very rare, now. The newer Fox 25BB Schnuerle came about as a stretch from a 19BB Schneurle, that but isn't in production. ..was only produced a few years...)

So, try 15% nitro (or more) with total oil around 25%, all or mostly castor. Around 9-4, 8-6 props should let it unload.

The Kap-Pak & Perfect tanks were not particularly good when new (as old as they all are now, chances are both you've tried have splits in the plumbing inside).  Get one of the recently produced clones of a Veco tank, 2 Ounce through 2 1/2 size, from Brodak, Eric Rule, or SIG.

Just got out and tried it today and yes it works fine now I don't know what helped more the new tank or the new case but no burp and no stall.  I think I can see a crack in the old case, which might explain the wide 2x4 and burp but the inverted problem may have been the tank I haven't opened it up yet to find out yet.
Thanks to all who tried to help (I need all I can get).