Okay... Diagnosis=Vapor Lock.... NOW WHAT?

[kimchee]

I am a newbie to this board, but I am quite familiar with how annoying it is when a newbie asks questions which can easily be answered with some reading... I HAVE DONE THAT TWICE !!!<br /><br />I have a I/O mercruiser 5/7L 8cyl small block engine with a 4bbl carb. I am pretty sure I have what people have referred to as vapor lock... I know this because I can VERY EASILY start when cold, but after approx. 45 minutes of riding, it becomes almost impossible to start... If I use water cooled towels to cover the metal gas tube a couple of minutes and properly ventilate the bilge I can avoid the hard start...<br /><br />NOW, the gracious people on this board have recommended the following.<br />- ventilate the engine compartment as much as possible. and cool down gas intake with water cooled towel.<br />- possibly replace METAL gas intake with a rubber gas intake??? However others have suggested, this could be VERY DANGEROUS, thus requiring further discussion.<br /><br />My point is, is that SURELY, there must be a permanent fix, what is it?<br />Is it a matter of using a particular fuel?<br />rebuilding the carbuerator?<br />wrapping the metal gas intake with insulation?<br />adding another blower, but I think this can't possible help enough...?<br />adding a clamshell vent opening to swallow up air, but I am concerned about the saltwater getting in...?<br /><br />PLEASE HELP !!! I read that vapor lock was common... How have you all conteracted this?

 

[JB]

Re: Okay... Diagnosis=Vapor Lock.... NOW WHAT?

You may have read a lot, kimchee, but not the title of this forum. <br /><br />Moving you to Mecruisers.

 

[Silvertip]

Re: Okay... Diagnosis=Vapor Lock.... NOW WHAT?

You may not have vapor lock. Carbs can develop porous castings that allow fuel to makes its way into the manifold during the "heat soak" period. Try starting with the thottle wide open to give the engine extra air. If it is vapor lock, check the routing of the fuel line and install a heat baffle that creates a gap of about and inch between the line and the shield, and between the shield and source of the heat. This need be only a shield made of thin aluminum. Wrapping the fuel line with flame resistent insulation may also help. Venting the engine bay is a matter or orienting additional vents such that forward movement of the boat causes air to enter the engine bay. Additional vents should be placed so the heated air can escape. Additional exhaust fans could help especially when running at slower speeds when forced air doesn't ventilate the bay. A temp sensor could be installed to start the blowers when bay temps get to a certain level. A phenolic spacer (if one is not already installed) placed between the carb and manifold also helps isolate engine heat from the carb. Last resort is to install a cool can like the racers do. Its a container in which the fuel line (metal) is coiled several layers high. The can is filled with ice to keep the fuel cold just before it enters the carb. In a boat, one could go a step farther and simply plumb a pump and water pickup line to the can and run water around the coils.

 

[bigbrownbuku]

Re: Okay... Diagnosis=Vapor Lock.... NOW WHAT?

a few possibly simple fixes.<br /><br />increase your engine bay ventilation to keep the area temp down.<br /><br />you can buy coast guard certified rubber fuel hoses with crimped ends.<br /><br />does your carb have a spacer to the manifold. composite spacers are avaialble to prevent heat soak.<br /><br />your main aim should be the engine area temperature, keeping the ambient temp around your engine lower might just solve your problem. do things like running with the hatch slightly ajar( making sure it isnt going to fly open while travelling) to see if it helps before you go drilling holes everywhere fitting vents.

 

[pra100]

Re: Okay... Diagnosis=Vapor Lock.... NOW WHAT?

I was having the same problem with my 4.3 cobra.My boat had one 3" bilge blower.I removed it and added a 4" blower.Then I added a 4" blower to blow air into the compartment at top opff engine..I also got a 2 1/2 x 17" vent and cut a hole for it in the front of my engine compartment.Solved my problem.I will add I tried the heat spacer under carb(holley 4 bbl.) and I put aluminum spacers behind my metal fuel lines to get them away from engine.These 2 things did not help.<br />The way I found my problem was my engine compartment is 2 piece,bottom and top.I took top half off and left it at home.Ran boat with just bottom half all day,stopping and starting.I had no vapor lock this way.

 

[catiiid]

Re: Okay... Diagnosis=Vapor Lock.... NOW WHAT?

Another simple thing to check is your fuel tank vents. If it is plugged up and creating a vacumn or negative pressure condition it is much easier to create vapor lock.<br /><br />ED

 

[kimchee]

Re: Okay... Diagnosis=Vapor Lock.... NOW WHAT?

Wow... First off let me thank everyone for there time in responding so quickly... THANK YOU ...<br /><br />I received alot of great ideas from everyone and will begin to explore immediately... But it seems that the recurring theme of the recommendations is to decrease the "ABIENT TEMPERATURE" of the engine compartment... Therefore I will further explore vents... But I like the CG approved rubber lines idea too... SO I will also be looking into that as well...<br /><br />Can anyone please post to let others know if they indeed used CG rubber lines INSTEAD of the metal ones? I am curious to know if those are working OKAY... <br /><br />Other ideas mentioned simply seemed beyond my skill level to perform... Although I am sure that future readers will APPRECIATE this thread...