2slow,
Don't get me wrong here as I don't mean to argue, but changing the tank/ carb alignment slightly(assuming it is wrong in the first place)will not fix the problem in his case. Come, let me tell my tales of woe...

I have tried all conceivable combinations- tank high, tank low, tank level...big tubing, small tubing, no tubing... all to no avail. I must say you are fortunate to not have this problem with your setup!!! But according to lefnut's description(and his solution), lack of back pressure is most certainly the cause. It runs fine when it is level, dies nose up or down, needle valve mostly out, etc. If it was anything more than a teeny tiny air leak, then his and my engines would still be having problems. I would still check for them, however... especially the carb plug, base, amd clamp. It would be even worse to have both problems going on!
Depending on what pitts/ engine combo you use, you can run into a problem of too little back pressure sometimes. The outlets are not always carefully sized or tested in development. I am not saying that it will always be the case, but it was the problem with both of my new Evolution engines when used with a pitts (Bisson brand). The ran great with the stock muffler, both in the plane and on the stand, but the pitts gave it trouble. With the pitts it would run in a level position as you said it would, but as soon as I tipped the nose up or down it would lean out or flood, respectively, and die. It acted exactly like what happens when your muffler pressure line is disconnected. And to get it to run in a level position the needle valve would be almost comletely out! The fuel tank position was correct, and there were no leaks. It did the same on a test mount. The fuel draw is just poor on these engines without pressure... probably something to do with that remote needle setup. After replacing and moving around various fuel system components and checking for leaks(even tried a fuel pump), I finally consulted the manufacturer of the pitts muffler. They stated that back pressure was probably insufficient for and suggested plugging one outlet and checking the result. That confirmed it for me. I didn't plug it though, I just crimped 'em down somewhat. Now after all this I have not had a single deadstick and it has amazing power... it pulls my p-40 like crazy, scaring me and anyone in the area. Oh yeah, it is pretty loud. No baffle was in the stock muffler was found.

For the record, I was just letting y'all know my personal experiences with these engines, and I don't mean to offend or claim to be a super glow god know it all. I wish I was... I would have figured it out before a million deadsticks and yanking all of my hair out! FLY SAFE and HAVE FUN

whew! long post sorry