Main passage plug in carb

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  • Bob N
    Senior Member
    • Jul 2005
    • 60
    #1

    Main passage plug in carb

    Don,

    Would it be possible to temporarily replace the main passage plug in the carb with a hose barb with tubing attached to flush gas through the carb? What size barb would fit? I am leary of running gas into a cup or jar, since there seems to be a 100% chance of spilling it into the bilge. Access to the carb is pretty tight in my Pearson 33. Just draining the carb for the winter sets off my my "gas sniffer."

    A second, unrelated question: What are the symptoms of a stuck valve (besides loss of compression)? I assume rough running? Loss of power so that the engine stalls when shifted into gear? That happened when I launched in the spring and once this summer, but in each case went away after a short time letting the engine idle. I shot a liberal dose of MMO into the cylinders through the spark plug holes when I winterized the engine last week.

    Bob N.
    Tags: None
  • Don Moyer
    • Oct 2004
    • 2823
    #2
    Bob,

    It would be very difficult to match the fine machine threads in the main passageway. However, you should be able to drill and tap the middle of the plug itself with 1/8" pipe threads and install a nipple and valve in the plug. If this works, it would make a good follow up posting.

    Stuck valves will result in "0" compression in their respective cylinders. As you suggest, they can stick in the beginning and then loosen up as the engine warms up.

    Don

    Comment

    • sastanley
      Afourian MVP
      • Sep 2008
      • 7030
      #3
      main passage threads

      I almost buggered mine up this weekend trying to get the main jet out when cleaning the carb...I would need to modify the screwdriver to get deep enough in and bite on the jet without damaging the threads..I was able to get the plug back in without damage to the threads, so I opted to go buy a gallon of carb soaker at the autoparts store.

      These jets seem a little bit fragile (soft)...none of mine really want to move without excessive force, so #1, I don't want to break/damage them, and #2, I also don't know the ramifications of each jet's settings, so I am content to leave them all alone for now. It looks like I'd need 4 or 5 screwdrivers all ground a little differently to match the various jets in the carb.
      -Shawn
      "Holiday" - '89 Alura 35 #109
      "Twice Around" - '77 C-30, #511 with original A-4 & MMI manifold - SOLD! (no longer a two boat owner!!)
      sigpic

      Comment

      • Al Schober
        Afourian MVP
        • Jul 2009
        • 2024
        #4
        The threads for the plug over the main jet are 3/8-24, straight thread - just like the top end of a head stud. Do not try to tap the carb body to 1/8 NPT - the dia is about the same but the pitch is different and you'll just end up with a mess. If you really want to get a hose connection into that port, the best bet I see is to find a 3/8-24 brass screw (hex head?) and then drill that out to 3/16 for a piece of 3/16 OD metal tube, epoxied in place. Then install a piece of 3/16 ID tygon tubing.

        Comment

        • Dave Neptune
          Afourian MVP, Professor Emeritus
          • Jan 2007
          • 5050
          #5
          Easy there

          Bob, careful with this! Al has a good idea if you really want to do this however I would use an extra "plug to do the modification" as sealing will still be a problem with STRAIGHT threads as the gasket on the plug is the seal.

          Are you just wanting to drain the carb or the tank? If it is the tank why go through the carb and have it possibly gather more KRAP in the carb?

          Yes it is not uncommon for sticky valves to work loose after a bit of running. I suggest a bit of top oil in the fuel at around a 100 to 1(a good two stroke oil or MMO) mix for a bit to get the oil on the valve stems while running. Often there is just a bit of build up in the guide and the additional oili will help to flush it out. I also prefer using a spray for going into the cylinders as the spray get all over wheras when pooring in a bit the oil is only going where gravity takes it ~ remember Newton.

          Dave neptune

          Comment

          • roadnsky
            Afourian MVP
            • Dec 2008
            • 3127
            #6
            Attention Class

            Note that Bob's OP is 4 years old. (11/16/2008)
            -Jerry

            'Lone Ranger'
            sigpic
            1978 RANGER 30

            Comment

            • Dave Neptune
              Afourian MVP, Professor Emeritus
              • Jan 2007
              • 5050
              #7
              Cha-ching

              Thanx Jerry, for pointing out that it's a Monday and I was up to darn early.

              Oops Dave Neptune

              Comment

              • roadnsky
                Afourian MVP
                • Dec 2008
                • 3127
                #8
                Originally posted by Dave Neptune View Post
                Thanx Jerry, for pointing out that it's a Monday and I was up to darn early.

                Oops Dave Neptune
                I do it all the time!
                AND, it doesn't have to be Monday.

                ...although usually an Adult Beverage is involved.
                -Jerry

                'Lone Ranger'
                sigpic
                1978 RANGER 30

                Comment

                • Bob N
                  Senior Member
                  • Jul 2005
                  • 60
                  #9
                  Always listen to Don

                  Yes, I took Don's sage advice. (Though I still hate draining gas though the main passage plug.)

                  Comment

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