i have twin 502s 1999 which seems to have vapor lock problems if i run boat hard and stop let set 1/2 hr sometime very hard to start bleed fuel rail then starts ok

Common problem with the 454/502 MPI mags. Do a search merc had a bulletin out about it. I beleve it was let it idle for x minutes before shutting it down and leave the hatch open to let air in to cool things down.

thanks for helping me

No problem us Iowa people have to stick together.

Heres the bulletin

http://www.outdrives.com/bulletin/se...9/mcsb997x.pdf

Merc has a one way valve "update" to keep hot water from flowing out of block to fuel cooler. I have seen this fix work, search merc website. Valve is around 90.00,good luck.

does it have a fuel return from the pressure regulator? if it doesn't, maybe try putting one on, i would think that by constantly having the fuel circulating, it'll never be given the chance to absorb the heat and vaporize, therefor you'll avoid your vapor-lock... if you have efi, for this system to work tho, you'll probably have to move the regulator to the OTHER fuel rail, basically the fuel flows in one rail, crosses over to the other rail, hits the regulator which pressurizes the system, and then bleeds off the excess fuel back to the return.... it's actually a very simple and efficient setup...

if you're carbed, then don't worry, just throw a regulator on AT THE CARB (meaning don't have it screwed into the side of the engine compartment with a long fuel line running to the engine) a fuel pressure regulator SHOULD ALWAYS be as close to the fuel bowls as possible, then just run a return line back to the tank.... should work like a charm!