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Mercury 700 vapor lock problems

Old 07-10-2012, 06:57 AM
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Originally Posted by ar300johnson
Running fuel with no ethanol makes a major difference in starting all kinds of engines in hot weather. Get rid of the ethanol crap and only use non ethanol fuel in your boat. I bet that simple step will cure your problem and will be quick, easy and cheap to try. Check puregas.org to find non ethanol 93 octane fuel near you.

And how exactly do you make sure all the marinas and lakes have non ethanol fuel?

Getting rid of ethanol is not that simple.

Link doesn't work.

Uncle Dave

Last edited by Uncle Dave; 07-10-2012 at 08:02 AM.
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Old 07-10-2012, 07:22 AM
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I know you're probably looking for 700 specific answers, but I've heard of a LOT of people in our area having vapor lock symptoms during the past 2 weeks (on multiple different engines). This heat in our area has been brutal, but relief is on the way this week. I hope you see the relief too.

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Originally Posted by smithimports.com
My 2007 Mercury 700's have vapor lock issues. It has gone from bad to worse. The other day it vapor locked just idling in a no wake zone and would not start till the next day. Anyone have thoughts on this. It was 102 degree outside when this happen but it happened when it was running. Both engine are having the same problem now. What's up with this Andy Smith
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Old 07-10-2012, 08:01 AM
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Originally Posted by PremierPOWER
I had (and probably still have) this same problem. Triple 700's and all three were hard to start after a run. Very frustrating and embarrassing. I posted and got a lot of good recommendations. One recommendation was to leave the hatch open after the run. Since this was easy, I tried it the very next day. Although it made a difference, the engines were still difficult to start. I have mechanical fuel pressure gauges and also the race view. I was concerned that the fuel regulators were not holding good pressure during cranking. I replaced the fuel regulators and that made a big difference, but the engines are still somewhat hard to start. The other recommendations that I received were more involved. I stumbled on 39 Unlimited’s post when he was experiencing problems. I talked with him and I am convinced that the re-flash is a good way to fix this. It will also help me because I then I will be able to use 89 gas. At that time, the winter run season was about over so I have not done this yet and I have the donzi is in for an extensive refit. I will probably try to get this done by the fall season.
The re-flash works like a champ. 89 non ethanol is fairly easy to find. Think Merc said the 700"s still pump out slightly over 700hp with ECU change.
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Old 07-11-2012, 09:35 PM
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Sorry about the link. Should have been pure-gas.org. I guess that you can only ask whether or not fuel has ethanol added. If you ever get a big load of bad ethanol fuel, you will take just about any step to avoid getting another load of that crap.
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Old 07-12-2012, 11:05 AM
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What does Mercury say? Has anyone called them? Maybe there's a simple modification to the fuel cooling/recirculation system that will solve this...
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Old 07-12-2012, 12:15 PM
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Originally Posted by C_Spray
What does Mercury say? Has anyone called them? Maybe there's a simple modification to the fuel cooling/recirculation system that will solve this...
someone please do...I am curious as to what they have to say.
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Old 07-12-2012, 07:31 PM
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My friend Has a 42 fountain with 700's that had the same problem even with 89 so we started lifting the hatch and leaving the blower on at idle or even at the dock now no issues at all
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Old 07-12-2012, 07:36 PM
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someone from mercury told me this when i was having problems, and it worked every time:

1) never shut the motors off immediately after running them. let them idle.

2) when cycling the switch on/off (as mentioned in an earlier post), push the throttles all the way forward. when trying to start after 3-4 cycles of fuel pump/switch, it may 'girgle' vs. start. if so, repeat and the motors always started.

(I remember it was more difficult when I jumped in to help a guy in an OL. they only have one key switch, i believe. i started one motor, let it idle for a couple minutes, shut it off, cycled the other motor, let it idle after it started, shut it off and then both recranked w/ no problem. he was amazed.
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Old 07-12-2012, 08:16 PM
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Originally Posted by C_Spray
What does Mercury say? Has anyone called them? Maybe there's a simple modification to the fuel cooling/recirculation system that will solve this...
I called Mercury....they told me to read the owners manual which said 89 octane. New 700's were designed to run on lower octane which is what I did and posted results. They now start just like my 525's did at any temperature. Try it you'll like it.
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Old 07-12-2012, 09:27 PM
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Does the 700 recirculate the fuel back to the filter head/dead head????

Seems like it mostly Fountains


My Buddy's 38 Formula did it all time. 500efis, he put a outboard fuel squeeze bulb (5/16) on it to pump when it does it so far he hasn't leaned out
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