ORIGINAL: opjose
Pumpers are great for the reasons already stated. Set the engine for maximum performance and forget about nose up tests, etc... the pump keeps things going.
Most Gasoline engines have a built in fuel pump as a point of reference.
As stated rebuilding the pump adds a small degree of complexity, and some additional cost... plus it is one more thing that can go wrong ( hint: FUEL FILTERS help keep debris out of the pump ).
However I really like them.
You can't rebuild an OS pump. Even if you were able to get it apart there are no parts for it to do a rebuild. OS will not just sell you a regulator diaphragm so you can't rebuild that either. As much as I like my OS engines this is one of the reasons I quit buying them new. I do pick up used ones and rebuild them though, pumps or no pumps. I have never paid more then $100.00 for one, that's my top price.