Hard start when hot.
 

454 mpi with B&M blowers, Motors start well and now idle well with no stalling. But the starboard motor won't start after it sits for approximately 1/2 hr. without a lot of coaxing. When it does start you have to rev it until it settles in and then idles fine. The port motor starts fine everytime. If you turn motor off and then restart right away it starts fine. Any help out there?

check the carbs on that motor sounds like it may have a bad seat, float or vent and may be flooding the motor.

Good advise from Just Once. Also, check the fuel system to be sure the fuel isn't draining back through the pump. Check for hot blower, also. Good Luck!!!

Forgot to mention, these are efi motors, sorry. With electric pumps

I don't know much about blower motors, but I know that Merc. EFI motors have an occassional problem with vapor lock. Maybe you should try running the blowers and leave the hatch cracked open for a while after a run, to let out some hot air. I always do with mine.

ok are these the B&M 250 blowers that bolt to the factory intake[remove the upper intake and use's the lower part] if so they are used on the 454mag and 502mag mpi's only, what year are your engines? if I remember the first kits had the ECM's mapped byFlagship marine, they used the MEFI1 ecm,s which do not have a good map for boost???? some people are changing to MEFI3 ecm's and rewiring the factory harness to fit[ swap the pins in the connector] but you sound like a vapor lock problem, maybe, switch fuels, also run a higher octane fuel and see if that helps, some fuels out there have a low reed vapor which will boil easy, don't know if this helps any, maybe some more info from you will help out

Make sure that you've got clean fuel filters....

Mike

Do you smell raw fuel as your cranking it over, probably not, then it is not flooding. What is the temp on both motors when you stop and start?

Injector is leaking or motor is vapor locking. Do you have fuel pressure gauges? If so does fuel pressure come up as soon as you turn key on? If pressure comes right up then problem is a leaking injector.

Mine use to do that as well. For a couple years merc use to have the return line go back to the water/fuel seperator. I removed the line and had the return go directly to the tank. then I blocked of the return to the seperator with a plug. It never happened again:)
Good luck