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Vapor lock?

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Wasabi757

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I’m finding that if I run at cruise speed (high power setting) for, say, a hour or so, then shut down for about a hr, that my boat will start and idle for maybe a minute then die. It then takes many attempts to start the engine but does eventually start and runs perfectly fine afterwards.I’m thinking this is classic vapor lock. Contributing conditions are high ambient temperature and ethanol in the gas, which I will no longer be using. I will probably alter my driving habits by reducing power for several minutes to idle before shut down and opening the engine hatch to allow the e compartment to cool.
Anybody else experience this? If so, how did you address the problem?
2005 Ebbtide 5.7L (350ci)
 
if you shut it down after a a long run, its very likely you are having vapor problems...especially if you have a small and tight engine room....

a cool down of several minutes, at a high idle, in neutral can only help...as does opening the hatch. Going with ethanol free gasoline will help but not eliminate the issue...

inadequate ventilation is the main cause on most small boats...few hull makers satisfy the engine maker's requirements for max operating temperature...most don't want to see anything over 150 deg F, in the engine room, over the top of the engine...
 
makomark said:
if you shut it down after a a long run, its very likely you are having vapor problems...especially if you have a small and tight engine room....

a cool down of several minutes, at a high idle, in neutral can only help...as does opening the hatch. Going with ethanol free gasoline will help but not eliminate the issue...

inadequate ventilation is the main cause on most small boats...few hull makers satisfy the engine maker's requirements for max operating temperature...most don't want to see anything over 150 deg F, in the engine room, over the top of the engine...
Click to expand...
Yes, I do agree we have a vapor locking condition. As soon as my existing fuel supply gets close to empty, I will refuel with gas that is ethanol free. I’m also going to be monitoring the engine compartment temperatures as well as keeping tabs on ambient air temperature while running around on the lake. Opening the engine cover hatch and venting out the heat coming off the engine has got to be a step in the right direction too. Perhaps a 12 volt fan/blower can be added to help get the hot air out as well.
 
You should already have a 12-volt fan/blower installed, required for boats with gas tanks in an enclosed compartment.
 
I do have a blower. Traditionally, I would run it only before starting the engine. I think I will run it while underway and leave it on after shut down. My guess it doesn’t use a lot of battery to run it after shut down. I’m also going to start monitoring the temperatures inside the engine compartment
 
I read that shortening the fuel line as much as possible could help prevent vapor lock? I've got a 98 Searay with the 5.0 Merc. The fuel line runs to the side of the compartment through a bracket and then loops back to the fuel pump. Guessing that is for a reason???
 
I'm thinking about what i can do to reduce/eliminate vapor lock on mine too.
Has anyone looked into hooking up a 3-port fuel filter and dumping the vapor outlet port back to the tank? I'm also thinking that replacing the steel line with rubber between the pump and the carb might help as well (or even insulating the steel line might help too).
I tried searching for links on this topic but didn't come up with much.
Vapor lock is common on carburated cars and these ideas have worked for many people.
 
I installed a pair of 3x8 ( hole size) louvered vents in the engine box on either side of the engine at the carb location.
 
Like Capt Bob suggests, air is your friend.

I don't think your car ideas will work on the boat...its engine compartment is not open to the environment at the bottom so ventilation is the only option...some are happy with a passive setup - some need more.
 
Wasabi757 said:
I’m finding that if I run at cruise speed (high power setting) for, say, a hour or so, then shut down for about a hr, that my boat will start and idle for maybe a minute then die. It then takes many attempts to start the engine but does eventually start and runs perfectly fine afterwards.I’m thinking this is classic vapor lock. Contributing conditions are high ambient temperature and ethanol in the gas, which I will no longer be using. I will probably alter my driving habits by reducing power for several minutes to idle before shut down and opening the engine hatch to allow the e compartment to cool.
Anybody else experience this? If so, how did you address the problem?
2005 Ebbtide 5.7L (350ci)
Click to expand...
pferat said:
I'm thinking about what i can do to reduce/eliminate vapor lock on mine too.
Has anyone looked into hooking up a 3-port fuel filter and dumping the vapor outlet port back to the tank? I'm also thinking that replacing the steel line with rubber between the pump and the carb might help as well (or even insulating the steel line might help too).
I tried searching for links on this topic but didn't come up with much.
Vapor lock is common on carburated cars and these ideas have worked for many people.
Click to expand...
I’m having the same issues with a two stroke. Was thinking about the 3 port filter also. Did you ever find a solution?
 
Interesting
I have a Pre Vortec 4.3 with the 4 BBL Quadrajet, and these have an exhaust crossover in the intake manifold for the heated choke coil and even running E10 gas I have never had vapor lock. The Vortec engines don’t have that exhaust crossover. Even after running on plane etc if the engine is shut off it will restart instantly.
I would look into your engine compartment ventilation. I do run the blower before starting but also run it continuously. One thing I have noticed that’s worth checking; ideally the boat should have directional vents. The vent that the blower is connected to should face aft. The vent on the other side of the boat should face fwd and be connected to a hose that forces fresh air into the bilge. This helps natural ventilation as the boat is moving fwd, and there’s a pic in Chapman’s Boating showing this as correct ventilation. Will post it if I can find it.
Other things that can be done:
Use an insulating carb spacer that insulates it from the heat of the intake manifold. I think maybe I never had vapor lock because the Quadrajet used a much thicker carb gasket than either the Holley or Edelbrock/Weber carbs. Look in Jeg’s or Summit Racing.
You can also use insulating tape in the metal fuel line from the pump to the carb….
 
On the fuel line not in it!
I did this on an old Ford 302 that often vapor locked in the summer heat with the A/C on…
 
Wasabi757 said:
I do have a blower. Traditionally, I would run it only before starting the engine. I think I will run it while underway and leave it on after shut down. My guess it doesn’t use a lot of battery to run it after shut down. I’m also going to start monitoring the temperatures inside the engine compartment
Click to expand...
Have you thought about opening the engine cover slightly while the boat is sitting?
 
I just moved the fuel line further away from the block and vented the cowl. It’s a two stroke outboard so I’m thinking a fan isn’t an option. Maybe we can take it out tomorrow and see if it helps.
 
Also I have taken the cowl off while fishing and still had trouble so hopefully the fuel line is the problem it was very close to the block (almost touching) in a couple places and now it’s probably a inch and a half away.
 
Mercury150xr6 said:
could it be the switch box? It does act like the battery is weak when it’s warm and not wanting to start.
Click to expand...
yes any electrical connection where you are loosing voltage is not going to help. You may want to check for voltage drop while cranking at battery and at engine. Don't forget to check the ground cable as well.
 
Turned out I have cdm not cdi so no switch box. Not sure if something electronic is heating up and cause no spark there for cause in flooding. I’ve read a lot on google hoping to figure it out without just throwing parts and money at it.
 
Mercury150xr6 said:
Someone had posted about a three port gar filter and I was curious if it solved the problem.
Click to expand...

If your tank is inside of the hull, have you checked the vent, to see if it's clogged? To test this, open the gas cap while it struggles to run and if it improves, it should improve and you'll probably hear a whooshing sound as air is drawn into the tank.
 
jimn said:
If your tank is inside of the hull, have you checked the vent, to see if it's clogged? To test this, open the gas cap while it struggles to run and if it improves, it should improve and you'll probably hear a whooshing sound as air is drawn into the tank.
Click to expand...
I’ve tested and ruled that out
 
Have you tried to add fuel as it's starting to run badly? That's a good test, but you need to be careful and I DO NOT recommend using a steady spray of starting fluid. Actually, I don't like using that for anything.
 
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