Overtightening them can distort them too. Most are aluminum.

The boat builder has been talking to Merc and trying to get some answers. There was another boat with the same motor built just before mine and he is having the same problems. He also boats at the same lake. So far they just keep blaming the hot air temps causing the fuel to boil. I will look into everyone's suggestions while I wait to hear back. So cool that you all take time to respond.

Do you run the motor for a few at idle speed or just shut it down hot after wot runs? A few minutes at idle with the hatch cracked might help (maybe you are already doing this but just a thought)

do this:

1. push the throttles to the wood.
2. turn the ingition key, if you have one, on.
3. try to start the motor until it girgles and then stop.
4. pull the throttles all the way back.
5. repeat step 2 & 3.

*might take two or three times of repeating this until it fires. but, it usually works after the first attempt. if it does not start, do not attempt to keep starting it. immediately go back to step 1 and repeat process.

this works on 600 & 700's.

walla!!!!

Yup. I always let it idle and cool down.

I will give it a try. Does that just cycle the fuel? You would think they could fix this issue by now without having to do all that. I will update what did the trick

agree. i am surprised as well. a notable person told me about this trick and it never failed me, and i have actually helped several folks who i saw struggling at the dock to fire up, and another guy who was unscrewing certain parts on the motor to release the lock. this is MUCH easier and was fail proof on my 600 efi's.

i guy in an OL, with a fairly large ego was blocking me in at Gilbert's at the Key Largo stop on the Miami Boat Show PR and so I politely walked over and offered to help him start it up. he smugly told me to go ahead.... and so i did. it started in only a matter of a couple trys. BUT.... on the OL's (back then, at least), they only had one ignition switch. so, after the first motor fired up, i let it run for a minute or two before turning it off and repeating the process with motor 2, and then restarted motor 1.

hope this helps.

PS: it's been a while....

i forgot, turn the ignition key on and off 5 or so times, priming the motor, rather then just turning the ignition switch on and then trying to fire it with the throttles pushed to max throttle.

sorry --- old age.... 40's are not for amateurs!!! lol

I have nothing close to 600cs's but my 454 mag mpis did that even after I ran the fuel returns to tank. In speaking to Eddie Young, he said my next step should be to remove the fuel filter head off the block and get the fuel line that runs underneath the motor away from it.

While I am not familiar with the 600 fuel, your getting vapor lock (worse with ethanol or winter mix fuel) which is all heat related. I didnt have any issues with summer fuel (nonethanol) but winter mix I put in was giving me mild vapor lock.

Insurance: keep a bottle of sea foam in the boat and if happens, Pull filter off an fill back up.

On computer controlled marine engines you have 7 modes of engine operations and the clear flood mode is one of them but this is not active for ECM and PCM 555. It is active for MEFI systems. This is for if the engine gets flooded of fuel, it can be cleared by doing so - Advance the throttle to 1/2 min to 3/4 open. when the throttle position sensor reads between 50 % to 75 % at cranking rpm the ECM will not fire the fuel injectors at all. This allows air into the engine but no fuel so the can start basically as a non flooded engine. Once the engine starts and exceeds over 300 rpms the ECM cancels the clear mode and then enters running mode. Again not active on ECM 555 and PCM 555.

If you have to advance the throttle everytime to get your MPI marine engine started - you have a problem somewhere in the system. It can even be a sensor reading input to the ECM especially for the IAC and or coolant temp sensor and or the TPS sensor and of course fuel related problems can be adding to the list.