SignsUp, if I understand the intent of your question, in order to have redundant electric and mechanical pumps, you don't need an either/or setup. An electric fuel pump can be installed near the gas tank, and the output run to the mechanical fuel pump as normal. Fuel will flow through the electric pump, even if it is not turned on. Likewise, if the mechanical pump should get weak, the electric pump will push/flow fuel through the mechanical pump to the carb, just fine. This can be useful, since the electric pump (if controlled by a manual switch) can be used to prime the fuel system after a long rest, or to aid hot starting, etc. Here is a lengthy piece by Deve that describes what I am talking about (scroll down to "
Augmenting Your Existing Mechanical Pump").
One thing to keep in mind, if the mechanical pump diaphragm should fail, it is possible for the electric pump to introduce fuel into the crankcase. Something to think about.
Hope this helps!
