Use of fuel booster pump with IO-360 engines
 

The POHs of some (most?) aircraft with Lycoming IO-360 engines require the booster pump to be On for takeoff and landing whereas others require it to be Off. Specifically, the Cap10b/c POH requires the pump to be Off for all operations except priming and emergencies. Presumably it can't cause an over-rich situation so why not have it on at times when losing the engine would be an embarrassment?

HFD

It is not the engine but the fuel system of the particular aircraft that determines whether the boost pump should be on or not.

As a general rule, if the boost pump is down stream of the primary fuel pump, it CAN lead to an over-rich mixture, and is therefore left off. If it is upstream, the final fuel pressure is still regulated by the primary pump, and therefore it is safe to have the boost pump on as a back-up.

That's interesting, I hadn't realised that the pressure regulator was in the mechanical pump, and had assumed that the electrical pump was always before the mechanical pump. On the assumption that you know what you're talking about :p I'm a (slightly) wiser man!
Thanks.

HFD

Do not leave the boost pump on for takeoff on an IO-360 if the POH says to leve it off. It has led to engine failures due to over rich mixtures.