2004 Mercury 40 hp EFI, 4 stroke vapor lock????

RandyJ

Master Chief Petty Officer
Joined
Jun 13, 2002
Messages
808
I'm sure others have had this problem. I go for a long long ride about an hour or so away. Runs great all the way. After an hour or so I start to leave and it starts fine but dies when I put it in gear or may run a short distance then act like it's running out of gas. I don't see any air in the fuel filter and can pump the bulb till hard then it still doesn't changee the problem. I remove the fuel filter under the hood, put it back on then it usualy cranks right up and coughs a little then takes off and runs fine all the way home ... most of the time. I'm not real familiar with these motors so would appreciate some advice on where to start to attack this problem. Last year I never had an issue like this although I did have to replace the voltage regulator TWICE. Never have had any other problem. This is the second season i've had this motor. Otherwise I'm extremly happy with it and it does run great and the gas mileage is GREAT!
 

RandyJ

Master Chief Petty Officer
Joined
Jun 13, 2002
Messages
808
Never thought it would be a water or moisture issue since it runs fine. Seems the problem is the fuel getting hot and vaporizing in the canister or fuel pump or maybe even in the fuel lines. I know that some of these type engines have issues with heat from the exhaust cover plate behind the regulator causing the regulator to get hot and burn up (happened to me TWICE!) Now I am having recurring problems with the motor not wanting to start after a long run until it cools off a long time. When I bring it into dock it doesn't want to restart. When I first get in it the next morning it starts right up like a new one. When it won't start... If I loosen the filter or fuel line at the engine then use the bulb to pump cool fuel through it then it starts up and runs fine.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Hey Randy are you still having this problem? I may have a solution for you that worked for me.

Well sir, how about sharing it with the rest of us since I for one have never heard of vapor locking an outboard engine.

I can tell you how to do it with a 1971 400 (brake) hp, big block Chevy station wagon with 4 kids and an 18' boat loaded go the gills with camping gear on the highway running 60 MPH in July in 100* heat. Answer: Just put a fuel filter in front of the fuel pump, not after it! The pump sucking against the resistance of the filter element causes a vacuum, boiling the fuel, and fuel vapor won't run that rig!
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
It almost certainly won’t be vapour lock.
more likely fuel starvation, water contaminated or its drawing air in the fuel line.
Compression check it ASAP to rule out the worst case.
 

chanders

Cadet
Joined
Oct 16, 2014
Messages
14
replace the fuel line, you know the grey stuff. The alcohol deteriorates the inside. Replace the fuel filter and it will be fine.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
I'm sure others have had this problem. I go for a long long ride about an hour or so away. Runs great all the way. After an hour or so I start to leave and it starts fine but dies when I put it in gear or may run a short distance then act like it's running out of gas. I don't see any air in the fuel filter and can pump the bulb till hard then it still doesn't changee the problem. I remove the fuel filter under the hood, put it back on then it usualy cranks right up and coughs a little then takes off and runs fine all the way home ... most of the time. I'm not real familiar with these motors so would appreciate some advice on where to start to attack this problem. Last year I never had an issue like this although I did have to replace the voltage regulator TWICE. Never have had any other problem. This is the second season i've had this motor. Otherwise I'm extremly happy with it and it does run great and the gas mileage is GREAT!

While you had the fuel filter off, did you blow through it with your mouth? If you didn't, take it back off and do it. If your breath doesn't freely flow through it with minimum effort on your part it's clogged. BTDT and spent $1k and lots of time chasing ghosts when the problem was a clogged fuel filter....on a newly purchased used boat.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
I for one have never heard of vapor locking an outboard engine.
Merc had quite a few VL.problems.The 3 cylinder 650 when it first came out was notorious for this thus the change to water cooled fuel pump housing. The 80's XR2 150 was also bad about it as was the 40-70Hp models. Solution was to drill metering hole in checkvalve in fuel pump.Only the motors with black cowls had problems. Randy change the impeller and if you have the black fuel line in splashwell either change to grey or cover it up in bright sun. What is happening is fuel turning to vapor pressure and wont allow float in VST to open, unscrewing filter releases pressure...
 
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RandyJ

Master Chief Petty Officer
Joined
Jun 13, 2002
Messages
808
While you had the fuel filter off, did you blow through it with your mouth? If you didn't, take it back off and do it. If your breath doesn't freely flow through it with minimum effort on your part it's clogged. BTDT and spent $1k and lots of time chasing ghosts when the problem was a clogged fuel filter....on a newly purchased used boat.

My neighbor has a 2006 90 hp EFI doing the same thing. My next move will be to change the impeller. I sent an email to Mercury and got a reply telling me it is not vapor lock but that the fuel cooler is clogged. ..... that does kind of make sense... SAME THING THO. fuel gets hot and vaporizes then fuel pump won't pump. They suggested a 3/8 fuel line and various things to keep the fuel cool. If it had a way to remove the heat under the cowl that could solve the problem. I think I will try to remove the fuel cooler and see if it really has blockage. Some how the heat needs to be removed quickly for a reasonable start up.
 
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