At the track last night it would level off and loose power?

IMO, the timing curve is not right - but in and of itself I don't see that causing this type of drop off. I've raced mid 12s on a mild 340 and 175hp N2O though the single 5/16 and a stock pump. I've also fed a 500hp 440 through the 5/16 line with no issues. So it may not be fuel delivery, but may be the carb settings. You need to read up on checking float levels. It's pretty easy to do. Check and see the jetting and power valve ratings too.