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Hose from air silencer cover to intake manifold (with pictures)

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  • Hose from air silencer cover to intake manifold (with pictures)

    Hi All,

    I am trying to work out exactly what the hose from the air silencer cover to the intake manifold is for. Can any one offer some words of wisdom? (see attached pictures)

    To me it seems like it would be to suck excess fuel that forms in the bottom of the air silencer cover into the intake manifold. Which leads me to my next question...

    There seems to be an abnormal amount of half burnt fuel (i.e. not raw fuel...more oil than fuel) which collects in the bottom of the airsilencer cover and then drips out of the bottom of the cover where the join is. This then runs down over the engine and into the splashwell when the motor is tilted up. Should there be a gasket in between where the cover bolts onto the air silencer?

    My theory is that if there was a gasket it would allow the fuel build up a little and would then be sucked through the hose I mentioned above into the intake manifold (if that is actually the function of the hose)

    Any words of wisdom would be greatly appreciated as I am stabbing in the dark a little.

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  • #2
    Re: Hose from air silencer cover to intake manifold (with pictures)

    The hose is there to reduce fuel spit-back from carbs to drain down - get sucked back into intake.
    As for gaskets, you did not mention engine type/model/year.
    Go to shop.evinrude.com or here:
    http://www.*****************/parts/jo...rude-parts.php
    Then check the parts list.

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    • #3
      Re: Hose from air silencer cover to intake manifold (with pictures)

      That hose is there to recycle unburned fuel back into the bottom cylinder. Older (early 1970's) engines had carbs that always seemed to leak fuel. Many of those early airbox assemblies also did not come with a gasket, so they'd leak that excess fuel onto the lower cowling on a regular basis. OMC began using a cork gasket between the airbox covers in 1974, which reduced fuel leaking onto the lower cowling. That cork gasket is replaceable. From the looks of the side of your carb, your engine is from this approximate vintage (an older type model.)

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      • #4
        Re: Hose from air silencer cover to intake manifold (with pictures)

        Check your reed valves if you are getting alot of fuel there, it could be blowing back into the airbox.

        Just start the engine and look at the front throat of the carbs to see if it is blowing gas out, you should be able to do this with just a flashlight and not have to remove the box.
        GO IRISH!!!!

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        • #5
          Re: Hose from air silencer cover to intake manifold (with pictures)

          thanks guys...forgot to mention it is a 1972 evinrude 100hp. As "emdsapmgr" mentioned that they started putting a cork gasket, I might try to see if I can make something up (do you think some type of gasket sealer would work?). Would the cork gasket that "emdsapmgr" talks about from the '74 model fit the '72 model?

          Thanks again.

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          • #6
            Re: Hose from air silencer cover to intake manifold (with pictures)

            It looks like when they added the cork gasket that they changed the halves of the airbox-probably when the added some type of channel that the gasket would fit in. You could make one and hope it might work. If you tried to purchase a used airbox assembly from a later model, you'll need to check closely where the alum casting holds the throttle/shift cables-it is slightl different on the later ones. The cold-start primer solenoid mount seems to be the same.

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            • #7
              Re: Hose from air silencer cover to intake manifold (with pictures)

              I've got a '74 Evinrude 50hp and I've been wondering the same thing. I would get excess fuel all over. I saw in my manual the rubber plugs; haven't ordered them yet and still had no idea why they were needed until now. BUT 1*-how much fuel should the carbs be spitting out? I know it's not an exact measurement but there is a decent amount around carbs near the front after running it. 2*- Would the amount of fuel coming out of the carbs affect the performance or even give a rough idle, lets say that the plugs were in place, or does it even matter?

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              • #8
                Re: Hose from air silencer cover to intake manifold (with pictures)

                I've run a lot of these old engines and never felt that fuel leaking from the carbs was much of an issue when the engine was running level on the boat. They do tend to be messy, however... It did seem to be more of a problem when the engine was tilted up on the transom at the end of the day. Or when the engine was trimmed up for shallow water operation. It is possible that some fuel pressure may build up during the heat of the day-after running-then you can pull the fuel hose barb off the front of the engine to prevent fuel flow. Obviously, high float settings will add to this problem.

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                • #9
                  Re: Hose from air silencer cover to intake manifold (with pictures)

                  Related to this thread - My 70 hp 3 cyl was pouring gas out of the front of two carbs. I installed carb kits and that fixed most of the problem. Prior to the carb kits the engine smoked a lot, but with the carb kits smoke level is normal as compared to other motors.

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                  • #10
                    So question my cover to intake hose on my 18hp 73 evirude fastwin developed a hole in it my boat died on the lake an i notice this tube dry rotted and had a hole will this effect the running of the motor it will idle but as soon as i give it gas it dies

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                    • #11
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                      Originally posted by Rickspoint View Post
                      So question my cover to intake hose on my 18hp 73 evirude fastwin developed a hole in it my boat died on the lake an i notice this tube dry rotted and had a hole will this effect the running of the motor it will idle but as soon as i give it gas it dies
                      Rickspoint Welcome aboard.

                      This thread is about a 100 HP motor, not an 18 HP motor. Also it is 6 years old.

                      Please read the Help Tip on top of the page and start a new thread of your own.


                      Closed.
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