I get the idea you are possibly reversed on your loop terminology. If you are flying along level and take the airplane up and around in a loop that is an inside loop. Sounds like you are loosing the engine on outside loops, if the needle is on the top.

I do think your engine needs a bit more running time, and that may well solve your problem. Another possibility is tank position vertically. A lot of people have much better results with the tank set about 1/4 - 3/8 inch high. I've never found this necessary, but many others get good results out of high-mounted tanks.

Be sure you cap off the overflow vent before you start the engine. (I use a BB in a short piece fo fuel line. Don/t use a bolt, as it will leak air.) Otherwise the the tank is not a working uniflow and you can expect a poor run.

Hope this helps.
Jim