Have a 2000 Baja 342 Boss
twin Mercury 7.4 Mag MPI
At all speeds, the boat runs fantastic
When I shut the boat down or any length of time, the starboard motor will not start ?
It may start an hour later it may start a day later
I already changed the cap, rotor and distributor ignition module.
I have a new distributor pick up sensor, but I’m avoiding putting that in because I would have to pull the distributor
At this point, I’m not sure if it’s ignition or fuel at this point
Kind of thinking a vapor lock issue but just not sure
any assistance would be greatly appreciated

VST cool fuel system causing vapor lock possibly.

that pump should be right between the two engines the hottest part of the bilge, vent by raising the hatch while at rest and see if that helps

are you talking starts, stumbles and dies? Thats vapor lock. Cranks but wont even trry to fire? I would think more toward ignition .

Have you checked for spark? Pull a plug wire and see if you're getting any spark. Plenty of methods that won't short out your coil...or light you up!

Unless you get a direction of problem, you're dead in the water.

2000 year engines are Cool Fuel.

Most likely vapor lock. Pretty common issue. Does it turn over, sputter and then stall??? If you cycle the key several times to activate the fuel pumps and keep trying to start it in 2-3 second bursts, it should fire after several tries.

To help mitigate the issue:
Do not run Ethanol fuel. Run your blowers for 15 mins and crack your engine hatch after shutting the engines off.

Griff's advice is spot on. I have been dealing with this exact issue on the 7.4 mpi Cool Fuel L29 engine. I had the same kind of problems and some people say you can carry sea foam with you and fill the fuel water separator and cycle key and get it to fire, others say bleed the fuel rail schraeder valve. I had done some research and Mercury actually produced a kit to rectify this. I recently installed it and had 55 min of trouble free boating with multiple tests of shutting off while hot. It's absolutely heat and heat soak vapor lock. Blowers seem to really help and I ran it the entire time running boat and it was fine. Did a test where I did not run it and it still fired with the new pump added even with heat, but man when I opened the hatch it was HOT. I detailed how I added the pump in this thread. Def crack the hatch for a few to air out.

Restoring an old Velocity 22 Race Boat

I had gotten lucky that my friend at the Marina had one that they took off a boat that went to an Aeromotive/Whipple setup. I did curiously notice the same looking pump for about 90% off Merc Pricing was here so maybe worth trying if you are handy with fittings and mounting and such? 862264A7 is the original Mercury kit # for the "boost pump kit". I had gotten the ORB to AN/Push Lock fittings from Positive Performance.

https://ppcfittings.com/?srsltid=Afm...msC0jrt04Atj9B

https://www.highflowfuel.com/fuel-pu...0aAtkNEALw_wcB

https://www.highflowfuel.com/fuel-pu...fAdjINkvZluS15

DD,

Care to explain how this kit fixes the problem?

I have a friend with a new-to-him 502, and it’s suffering the vapor lock issue on a regular basis. It would appear this kit is compatible, but we’re just wondering what’s the magic with it. I’m guessing the instructions explain this, but where does one install the pump in the system?

Thanks. Brad.

I am quite far from a mechanical engineer or an engineer of any sort. But here’s my theory. Fuel turns to vapor around 120 ish degrees f.

I am assuming the fuel rail becomes air bound. When it cools back off, the fuel returns to a liquid and able to be pumped to rail and injectors expel the fuel and air mixture. I 100% notice a change in the noise of the cool fuel when it’s vapor locked (sounds like a water pump running dry) if you’ve ever used a transfer pump. I think the feed line with vapor almost becomes air bound. It seems like the secondary pump keeps pressure on the fuel filter towards the cool fuel and rail. Almost a “pusher” or “lift pump” to help it force to rail and past the air block.

It was described as a vapor lock kit by Mercury on the part number and it seems to do just that. It is however a very over priced kit as I listed above should be able to put one together under $300-$350 and mount it before the fuel filter. I was lucky enough to trade a case of beer for mine.

Take the feed line from tank and mount it to the one side and the feed of the new pump to the inlet on fuel filter housing. Let it keep pressure on the housing. If you click into the above link I posted how I mounted it. I am sure folks more qualified in petroleum feed engineering will chime in here or debunk my theory. All I can say if mercury sells it to solve a problem described as vapor lock and in my testing it sure worked. But Griff’s advice above is spot on, and free. Try those to start and a infrared thermometer is your friend in testing.

Guys,

Sorry for the detail, but it may be of some value to the OP….

So we’re working a theory…. The fuel line converts from rubber hose coming off the mechanical pump to 3/8” hard line, then connects to the HP fuel pump on top at the back of the engine. Assuming the vaporizing is occurring in the hard line adjacent to the valve cover, we are thinking about just bypassing the hard line altogether. But we need a fitting to connect to the HP fuel pump. I know we could cut and flare the hard line where we want it, but a conversion fitting would be a cleaner option. Anybody have an option for that?

Thanks. Brad.