Ive got twin 500 efi's in my boat and the port engine want hardly start and run after running it for a little while and then sitting around in the water when the air temperature gets above 100 degrees.Ive changed the fuel filters and even put a new fuel pump thinking that was the problem.Has anybody here on OSO had this kind of problem with there boat and if so what do I need to do to cure this?It runs fine when the air temp drops below 100 degrees......Puzzled.... Hank 36

vapor lock

Make sure you leave your hatch open when sitting around because the engine compartment just bakes and vapor locks. Had it happen many times.

Why doesn't my stbd engine do it?Kind of hard to leave the hatch up when it's covered with bikini's wanting to sun bath.

Hank, I was on Norris Lake this weekend and there were many vapor locking incl. me.. I have read more sh-t on this than I care too I bet a 100 pages or more.. I have ran new S/S fuel lines, moved the water seperators off the motor,, even ran the return lines back to the tank.. Still did it.. I'm going to insulate the lines next.. But they are right, run your blowers for 1/2 hr at least but best yet is let the heat escape by lifting the hatch.. I lifted mine for 15 min. while everone was swimming and drinking yoohoo. and it helped a bunch.. If you want a laugh call mercruiser on this. They have more excuses and blame the boats mfg..
There is a perm. fix with the Aeromotive pumps but get ready to spend the $$..Thats my next step.

I'm willing to bet you have a 2000 or 2001 motors and I was going to say port engine on a twin but you already stated that. In 2002 Merc went to a mechanical AND electric pump to help correct this problem.

t500hp they had been doing that for years w/ the regular 502 efi's w/ the mechanical & electric. I have the black 502 efi's & have had serious issues w/ what seems like vapor lock. The issue thats driving me crazy is after a long idle I go to get going & the motor will shut off before getting over 2000rpm's, open the hatch play the waiting game it fires up & 9 out 10 times it runs perfecty fine after that....

Have any of you had this problem of getting them running then it shutting off?

Thanks everyone for your input.My engines are 2001 models with the single electric fuel pump in the fuel cool box.I talked to a local mercruiser mechanic Today and he informed me that mercuiser has a inline valve system thats been developed that holds water in the upper part of the motor to absorb the heat to reduce the vaporazation of the gas in the fuel lines and rail system.It cost about $125.00 and I guess I'll give that a try because I was told to do all the things that you guys have done or mentioned in your post unless someone's tried that fix with out success.What I don't understand is why the stbd engine doesn't do it.One thing for sure the Merc Tech hotline is a joke.

The port does in because the fuel line comes up between the engines....getting heat from both sides. The starboard does not because the fuel line is to the outside of the hull and only gets heat from the one engine.

Hank i've seen your 36 in Smith Bay at KY Lake a few times with out a doubt one of the best looking 36's i've ever seen! I had a 502Mag in my last boat (Baja) and it stranded me one to many times with vapor lock mine had a Whipple and i always took it to Young Performance Marine because no one near my home knew how to work on it. Anyway just call Eddie he fixed mine with some type of return fuel line to the tank it was relatively simple and didnt cost much, he can probably just explain it over the phone. My 502 never vapor locked again.

Because the water sep fuel filter on the port engine is between both engines and gets hotter causing the vapor lock condition. Merc makes a booster pump kit that will fix the issue.