Ken, I'd do as Rob said and insure your clunk setup is good(stuck or not too long)
I use all my fuel on every flight.. So mine will "rub" the middle/bottom of the
end of the tank, but can't get stuck and I also file the slit a bit bigger for those
times depending what tank.. I also add brass tubing to prevent the clunk from
going to the Frt.
I'm not sure about the OS 55, but I have been told the the FX 46 does not like to be
inverted with a higher tank... If your removing the tank for replacement, you could
trim the tank saddle and oblong the firewall hole to drop the tank somewhat, IIRC
I lowered mine about 1/2" or so then I just used silicon to hold and seal.. also I
mounted the engine inverted on the top of the up right engine mount(you may have
to "trim" one of the mounts arms) and gained a little upward movement of the carb
also, but it was for my S-82.... I used this tank, But it "could" have been the 12oz

http://www2.towerhobbies.com/cgi-bin...?&I=LXFU44&P=7

Another Great "Do" morning... I starting to go "Low" again... Might not be good if the
"past shows up [:@]... Gary, what do you use to cover up the scrape marks from the
runway on the top of the rudder?? [8D]