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4.3

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  • 4.3

    Starts and runs perfectly to 3200. Will run there all day. WOT to 4400 and slowly drops down as if running out of fuel. Everything to the QUADRAJET has been checked. Carter pump puts out way more than needed at the carb. Filter in carb has been removed. Thunderbolt ignition, timing is perfect. Had this problem for quite some time and now it is at the top of my list. What else to check? Thanks, Jerry
    1988 26' cuddy
    1975 20' open
    31 Grand Slam
    16' Sandpiper
    14' Certified Fiberglass

  • #2
    Could it be a vacuum leak? I dont have a lot of experience with this but i have been told to spray WD-40 around the perimeter of the intake or carb base to see. I also have been told you can hook up a vacuum gauge to the intake manifold which is "the easy way" but I have never been able to figure it out. Diesels are so much easier. Tough not being smart. I dont recommend it.
    '78 20ft Cuddy
    Mercruiser 350 FWC preVortec w/Carb

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    • #3
      Not sure what type of ignition you have but years ago had the same symptoms from a bad coil and another time from a bad condenser (though you may not have one if electronic). If you back it back down to 3200 does it run OK? (Mine would.) Another thought is vapor lock. Has anything changed so far as routing of fuel line? Has it just been an issue on these hot days we are having?
      C Rhodes
      26' Mackinaw - 1990
      351 Indmar (1990-2006: Great Engine)
      351 PCM (2006 - Current)
      Southport, NC

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      • #4
        Is this an AFB ? If so, check the little kidney shaped plates visible next to the choke. Hi speed jets in there, one may be clogged or spring broken not allowing full fuel. OOPS! Not an AFB..........duh
        Last edited by ARGO; 06-23-2018, 06:15 AM. Reason: stupid & can't read

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        • #5
          Jerry,
          Some of the fuel pick-ups in the tanks used to have a small mesh screen soldered on the tip to prevent debris from being sucked up. With the addition of the alcohol, sludge would build up around the screen causing problems with fuel flow. Maybe....
          Nay
          If it doesn't say SHAMROCK, it doesn't say much


          '85 Shamrock 17'
          '68 Bertram 20' Bahia Mar

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          • #6
            Everything from the tank to the carb has been checked. More fuel than needed at the carb. Never ethanol in this boat. Carb is coming off on Monday.
            1988 26' cuddy
            1975 20' open
            31 Grand Slam
            16' Sandpiper
            14' Certified Fiberglass

            Comment


            • #7
              Just got the call from the engine shop. The carb is perfect. He said to check the linkages. Something may be restricting the secondaries from opening all the way. Job for tomorrow.
              1988 26' cuddy
              1975 20' open
              31 Grand Slam
              16' Sandpiper
              14' Certified Fiberglass

              Comment


              • #8
                Carb is operating perfectly on the boat. Backfires through the intake and oil pressure is high. Just took the plugs out. [ It was only 125* on the deck.]. They all look good. Valve or lifter? Same problem since rebuild.
                1988 26' cuddy
                1975 20' open
                31 Grand Slam
                16' Sandpiper
                14' Certified Fiberglass

                Comment


                • #9
                  Try checking to verify that distributor is timed correctly and locked down.
                  Nay
                  If it doesn't say SHAMROCK, it doesn't say much


                  '85 Shamrock 17'
                  '68 Bertram 20' Bahia Mar

                  Comment


                  • #10
                    Timing is perfect. Valve covers coming off next.
                    1988 26' cuddy
                    1975 20' open
                    31 Grand Slam
                    16' Sandpiper
                    14' Certified Fiberglass

                    Comment


                    • #11
                      Do you have another cap and rotor to try?
                      Serenity
                      07 246 WA
                      5.7 MPI Crusader

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                      • #12
                        Not ignition. Plugs are perfect. Runs perfectly but runs out of fuel at high RPM. Plenty of fuel to carb but it seems that compression is keeping fuel from getting to cylinder. Make sense?
                        1988 26' cuddy
                        1975 20' open
                        31 Grand Slam
                        16' Sandpiper
                        14' Certified Fiberglass

                        Comment


                        • #13
                          When you did the rebuild, did you put in a new cam or re-use the old one?

                          Maybe going out on a limb with this...but maybe the high oil pressure indicates a restriction in the oil path after the sending unit and the valve train is starving for oil and running tight...getting enough oil to not seize but not enough to run freely????

                          Backfire through intake caused by slow to close intake valve?
                          1986 26' HT w/5.7 PCM 330HP RWC

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                          • #14
                            lifter or an exhaust valve not closing. Thats where I'm going now. Don't know on the cam.
                            1988 26' cuddy
                            1975 20' open
                            31 Grand Slam
                            16' Sandpiper
                            14' Certified Fiberglass

                            Comment


                            • #15
                              Valve covers off, looking at rocker arms going up and down. Have 2, next to each other that move exactly the same. Like they are on the same cam lobe. I'm no mechanic but, I don't think that is right.
                              1988 26' cuddy
                              1975 20' open
                              31 Grand Slam
                              16' Sandpiper
                              14' Certified Fiberglass

                              Comment

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