Help: '67 HiPo starts, but won't hold idle below 1500

The fule line should be a compression type seal, so usually no thread sealer (teflon tape) is required. You don't want the tapes to break up and get into your carb and clog jets etc. Were you careful to not cross thread when you bolted the fuel line back on? As long as it's threaded on properly, go ahead and tighten it some more and try to get it to seal. Remember that the brass fitting screws into the carb bowl, so make sure that is snugged (don't overtighten it, but make it good and snug) and then tighten the fuel line into the brass fitting while holding a wrench on both. If it still leaks, take it off and look at the end of the fuel line - it should be a flared fitting. If it's bent up, you will need to replace it because it will never form a seal.

BTW, you can remove the fuel bowls on the Streey Avenger carbs as they have reusable silicone gaskets. Just be careful and they should be fine.

The fuel line doesn't screw directly into the bowl, but into a fitting between the bowl and line. This has a thin rubber coated metal gasket ring between it and the bowl. When tightening the line, you'll have to first have the inner fitting tight, then hold backup with a 1" wrench while tightening the line. As the others have said, make sure you don't cross thread the line before screwing it all the way in. It should go almost all the way by hand and the last bit with a wrench. Don't sweat removing the bowls, buy a Holley quick kit before doing this though, it'll have new gaskets, powervalve and accellerator pump diaphram in the kit. Also when reinstalling the bowl screws, make certain the screw gaskets are in place and not doubled up with old gaskets. Holleys aren't complicated, but you do have to make note of how the parts and gaskets come off so as to reinstall everything correctly. I'm also 99% certain you haven't hurt anything but the gaskets by what you've already done, so don't be shy about going further.