... wouldn't a check valve in the bypass line help keep fuel pressure to the carb?
seems like with the electric pump running fuel pressure could be directed back towards the tank or back to the inlet side of the electric pump.
Correct. The install photo I showed is not actually 100% correct but will give an idea of how to install. There is a check valve in the electric pump by-pass line (shown directly above the pump itself).
With the install fashion shown the pump can be used either as a primer or full time.
- http://www.how-to-build-hotrods.com/electric-fuel-pump.html