I have a profile Cardinal that has the universal mount from Brodak so i have been trying different engines out. ST 46, LA 46, and others all run the way they are supposed to. Yesterday i mounted a Stalker 46 and had an issue with what sounds like it going dead rich when you point the nose down. Lap times were even so I'm pretty sure tank height is correct, prop was a XOAR 11 x 6 and Rev 11.5 x 5, both worked pretty well and lap times were 5.2 to 5.4  The engine breaks everywhere like it is supposed to EXCEPT like on down leg of outside squares and when you hit the turn to inverted on the reverse WO. As soon as you hit down it just seems to go really rich, like a burp but not a burp. It responds back pretty quickly and only seems to do it on the first turn...after that is seem OK. I tried uniflow with press, uniflow no press and vented, all about the same.

Set up is:
Stalker 46 SE (new ones from Tom Dixon) not sure if they are the same as the ones i had back inthe 90s. It is a baffle piston but I thought my old ones were iron piston..don't remember really
Thunderbolt RC long plug
RSM 4.5 oz uniflow tank
XOAR 11 x 6 prop
stock needle valve
stock venturi...not sure what size it is...yet, will measure tonite.

Where might this review be? Wouldn't mind reading that. I wonder if it was on profiles only or both inverted and side mounted...

Fuel used? That might make a difference. Some Stalker users around here used 80/18, no nitro, all Klotz. Others used "YS 20/20" (i.e., 20% nitro) because they needed more power.  Steve

I KNEW I was forgetting something in the set up part...fuel of course...of some importance DOH!
I actually was thinking this may have been the issue all along, I was using Powermaster 10/22. I don't have any all synthetic or low castor content fuel or I would have used it as i have read these like very little castor. Since i first posted I have gotten PMs about this engine and this issue. I put the engine in another plane in inverted mount and no burps, just the sweet stalker run i remember from the 90s. 

Interesting...If I remember correctly the Stalkers have the "screw in" back plate where the case is threaded female and the backplate threaded male, with little cut outs to get your tool in to pry/twist off, and an O ring or some kind of gasket back there. I will look tonite.