Originally Posted by bob_t

First generation of 500EFI's don't have a mechanical pump, just electric. They (later) added it due to major complaints of vapor lock. There are a couple of "easy", somewhat reliable ways to tell which generation 500EFI you have ... later ones have a "ball" on the end of the oil dipstick instead of the "curl". Also, the headers were changed ... early headers have a straight piece of rubber hose connecting the header to the tailpipe, later gen has a "U" shaped jumper hose. With the earlier version and straight hose, you had to either slide the header forward or the tailpipe aft, to get the header off. Later version, you just disconnect the "U" jumper hose and pull the header straight away from the engine (nice improvement !!). Usually, but not always, the earlier gen don't have the mechanical fuel pump, and the later versions always have the mech fuel pump. I always look to see which jumper hose is on the header to tell if it is an early, or later, version of the 500EFI. .... just some more "performance boat trivia"