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Vapor lock

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This weekend while at Lake Powell we were experiencing vapor lock in our jet boat. The boat is a 21' Commander with a carbureted 502. After a 1 hour run we parked at a beach and hung out for about 45 min. Loaded up, started up and made it 100' before it died. Opened the hatch and let it cool off and set a damp shirt on the fuel pump and fuel rails. 30 min later it stared. What could be done to prevent this? The engine has had 30 hours/3 trips on it before it stared doing this but this is the second time it's been in 100*+ weather. It did stall in front of RR a few weeks ago but it fired back up right away :point The electric fuel pump and filter are mounted on the back of the engine. Would moving the pump and filter off the engine to somewhere else like the transom reduce the heat soaking and prevent the vapor lock? Is there such thing as insulating the fuel lines to keep them from getting hot?
 

ddevore

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This weekend while at Lake Powell we were experiencing vapor lock in our jet boat. The boat is a 21' Commander with a carbureted 502. After a 1 hour run we parked at a beach and hung out for about 45 min. Loaded up, started up and made it 100' before it died. Opened the hatch and let it cool off and set a damp shirt on the fuel pump and fuel rails. 30 min later it stared. What could be done to prevent this? The engine has had 30 hours/3 trips on it before it stared doing this but this is the second time it's been in 100*+ weather. It did stall in front of RR a few weeks ago but it fired back up right away :point The electric fuel pump and filter are mounted on the back of the engine. Would moving the pump and filter off the engine to somewhere else like the transom reduce the heat soaking and prevent the vapor lock? Is there such thing as insulating the fuel lines to keep them from getting hot?

My Ultra with a 454 carbed does the same thing. For me I can run the fan when it's sitting out hot and it won't do it at all. If I dont and I notice it starting to fall on it's face I can generally feather the gas some for about 20-30 seconds when getting on a plane and I'm good. I tried moving the fuel pump / filetes back to the transom from the motor and no difference.
 

Quicksilver

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I am guessing the engine is covered? I know alot of people who open their engine covers when they are parked to cool off engine.
 

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The engine is covered. A week after powell I pulled the rear side panel off in the engine compartment and looked down the side at the tank to make sure the vents weren't messed with. (We are 3rd or 4th owners) I noticed some type of siphon device on the vent line and I think that may be the culprit creating a vacuum in the fuel tanks. Yesterday we were at Mohave and after a hour run we beached the boat and had the hatch up for 1.5 hours and when we left I switched tanks and it stalled from not getting fuel. Pulled the fuel cap and smacked the fuel pump and filter. Heared it prime and it fired up. We are going to tear into the vents and see if that fixes the problem.
 

guest hs

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Try this, before shutting your engine off let it idle for about 5 minutes, when you shut the engine off crack open your engine hatch about 12 inches and run your blower all the time. This should really remedy any vapor lock issues you might have
 

Quicksilver

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The engine is covered. A week after powell I pulled the rear side panel off in the engine compartment and looked down the side at the tank to make sure the vents weren't messed with. (We are 3rd or 4th owners) I noticed some type of siphon device on the vent line and I think that may be the culprit creating a vacuum in the fuel tanks. Yesterday we were at Mohave and after a hour run we beached the boat and had the hatch up for 1.5 hours and when we left I switched tanks and it stalled from not getting fuel. Pulled the fuel cap and smacked the fuel pump and filter. Heared it prime and it fired up. We are going to tear into the vents and see if that fixes the problem.

Ah. It sounds like the tank is not venting properly.
 

BHC Vic

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I was going to start a new thread but I saw this one. Can someone explain to me what vapor lock is? After talking with someone I think my boat may be experiencing this or maybe bad gas or maybe a combination?
 

RiverDave

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I was going to start a new thread but I saw this one. Can someone explain to me what vapor lock is? After talking with someone I think my boat may be experiencing this or maybe bad gas or maybe a combination?

Vapor lock is exactly what it sounds like V.. The fuel (liquid) gets warm enough that it changes into a gas state (vapor) while it's still in the fuel system. There's a lot more to it from here with lots of arguments that will likely happen.. But. If it turns to vapor the fuel pump can't pump the fuel so you lose fuel pressure and ultimately spark, which means the motor will stall, won't start, stumble etc.. Now in other instances maybe they ran a fuel line next to an exhaust or something which is heating up a portion of the fuel system.. The fuel can be gassing in that area, when it turns to "vapor" in that area it also causes the same problems even though the fuel pump is pumping liquid at the tank.



I would be highly surprised if your boat was experiencing vapor lock.. That being said last month between the humidity and the high temps A LOT of people were having vapor lock problems.

RD
 

BHC Vic

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Vapor lock is exactly what it sounds like V.. The fuel (liquid) gets warm enough that it changes into a gas state (vapor) while it's still in the fuel system. There's a lot more to it from here with lots of arguments that will likely happen.. But. If it turns to vapor the fuel pump can't pump the fuel so you lose fuel pressure and ultimately spark, which means the motor will stall, won't start, stumble etc.. Now in other instances maybe they ran a fuel line next to an exhaust or something which is heating up a portion of the fuel system.. The fuel can be gassing in that area, when it turns to "vapor" in that area it also causes the same problems even though the fuel pump is pumping liquid at the tank.



I would be highly surprised if your boat was experiencing vapor lock.. That being said last month between the humidity and the high temps A LOT of people were having vapor lock problems.

RD

Thanks Dave that makes perfect sense. After looking online I'm not even sure the 8.2 mag can vapor lock? I'm thinking now maybe a bad gas thing? Te boat fires up off the trailer and runs great. Afternoon it doesn't start first try and sometimes will start but won't idle. I'm going out this weekend to see what's up.
 

Shortdeck

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There's another thread on here that's suggest having an inline fuel pump, a booster pump, will help prevent vapor lock. I just went through this whole deal because my booster pump failed. It was rigged with the booster pump so I decided not to delete it.
On Aeromotives website there's a lot of info on how to prevent vapor lock and that today's fuel blend is more prone to vapor lock.
 

Shortdeck

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And with these newer boats, the fuel tanks are vented through a charcoal canister. Also not helping.
 

BHC Vic

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There's another thread on here that's suggest having an inline fuel pump, a booster pump, will help prevent vapor lock. I just went through this whole deal because my booster pump failed. It was rigged with the booster pump so I decided not to delete it.
On Aeromotives website there's a lot of info on how to prevent vapor lock and that today's fuel blend is more prone to vapor lock.

I think mine also has a booster pump. I need to speak w Jeff though. This weekend. I'm going to try starting w the blower on. I always forget. If that doesn't work maybe try opening the hatch? Not sure it's vapor lock though because eventually the boat starts. I'm guessing heat/cheap gas I dunno what I was told did make sense though. It's when the boat is hot or it's given me the most trouble after idling through the now wake zone.
 

racerden

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I was going to start a new thread but I saw this one. Can someone explain to me what vapor lock is? After talking with someone I think my boat may be experiencing this or maybe bad gas or maybe a combination?
Vapor lock occurs when gasoline gets hot enough to boil, thus turning to vapor. Although rare, it can occur downstream from the carb especially with hard lines that are routed close to a high heat source but most always it's at the carb area. A couple of validated reasons/ideas are:
1- Float level too high. Sounds opposite of principle however the more the fluid, the more heat it will retain especially after shutdown. Your post saying loading up 'may' support this direction especially if someone has recently gone thru the carb. Keep in mind our marine environment usually dictates a slightly lower float level than OEM automotive or carb manufacturer specs
2- Carb fiber spacers. These do a very good job of insulating and they aren't expensive. A spacer of no more than a 1/2" works very well and usually will not require any mount/hatch modifications.

Hope it helps,
DV
 
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