Announcement

Collapse

ONE RULE

Consider this your neighborhood bar,corner soap box, fish house, marina, coffee shop or anywhere else you go to hang out with friends and talk anything you want. Only thing, personal attacks will not be tolerated. No name calling or belittling. Be civil at all times and have fun. If a topic offends you, don't read any further.
See more
See less

Intermittent rpm

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Intermittent rpm

    I need some help. Boats been great running for 2 months. Get to my annual week long scallop trip and stop for gas turn the key..... no guages but still turn over. Buy a test light and chase that down to bad ignition. First time go to throttle up....wont go past 2500 rpm. Try it a couple times still wont get up. Stop and get ice 5 miles or so down river. Throttle up to go home to work..... runs like a champ. Run it out 20 miles no problems. Coming in the channel I go from 3000 down to 2000rpm. To pass someone. Bogs down again and wont go over 2500rpm. Hit the idle speeds the othe 5 miles in runs perfect.

    It is a little harder to start. Both tanks tried same problems. Brand new fuel 93oct filled in both tanks. Checked carb. Choke is opening. Linkage seems good. My first thoughts were fuel.....opened it up to wot and not starving for fuel.

    Any thoughts??

  • #2
    Engine is 351w pcm carbed

    Comment


    • #3
      Coil heating up? Always a pain to diagnose electrical intermittent stuff.
      Atlantic City, NJ
      1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

      Comment


      • #4
        Coil is warm.....not hot. Just tuned up. Coil less than a month old. Timing is set perfect.

        I thought electrical because washed and waxed inside and out. Believe that was fault of the ignition. Checked all grounds when chasing ignition.

        Comment


        • #5
          Heat causes connections to come and go depending on conditions like humidity, temp and who knows what else. Vibration? Because it comes and goes, that is my first suspicion.
          Atlantic City, NJ
          1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

          Comment


          • #6
            Make sure screen where fuel line goes into carb is clear. Dont ask me how I know that
            '78 20ft Cuddy
            Mercruiser 350 FWC preVortec w/Carb

            Comment


            • #7
              Run the boat yesterday. If I give it full throttle to get up on plane and its get past 2500-2600 rpm it will run fine. When running like this I can get it to wot and secondaries are opening. If I ease into the throttle it bogs down at 2300 and wont bogs down and cant get past there. I could run it pretty well yesterday as it was just me and my wife and it will jump on plane.

              Thanks I'll check the carb screen. I am thinking maybe some binding or something at the carb?

              Comment


              • #8
                Originally posted by cajunl View Post
                Coil is warm.....not hot. Just tuned up. Coil less than a month old. Timing is set perfect.

                I thought electrical because washed and waxed inside and out. Believe that was fault of the ignition. Checked all grounds when chasing ignition.
                Just because the coil is new-ish doesn't mean it couldn't be bad. Ask me how I know...
                C Rhodes
                26' Mackinaw - 1990
                351 Indmar (1990-2006: Great Engine)
                351 PCM (2006 - Current)
                Southport, NC

                Comment


                • #9
                  Yesterday, she definitely ran worse. I got 2 backfires and she is smoking like really running rich. Gonna do new coils and ballast resistor today and see if that helps. My ignition switch failed on the ignition side of the 3 studs. Gonna chase wire and grounds again

                  Comment


                  • #10
                    New, fuel filter, ballast resistor and coil. Thought I had her whipped as a test drive with just me and I could not get it bog down and no problems. Added 3 people with coolers and bogged down again at 2200 or so. So it seems to be an under load situation. Coil is cool. Old resistor was brittle. I bought what they had at napa and is a 2.8 ohm resistor....is this correct? The resistor is hot the coil is not. Is this normal?

                    Comment


                    • #11
                      Under load usually means timing, distributer advance or vacuum.
                      Atlantic City, NJ
                      1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

                      Comment


                      • #12
                        The resistor is a maybe. Some systems require one, others do not. Therefore it depends on what's in there. It is probably safe to say it needs one if there was one but never say never.
                        Atlantic City, NJ
                        1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

                        Comment


                        • #13
                          Thanks everyone. Went through and cleaned all the grounds, advanced the timing some, and adjusted the carb. Don't know which did the trick. When I adjusted the carb at home I did 6* at idle on the trailer. I gave it more. Don't know how much as I had to buy a cheapo light and did it mostly by ear anyway. But it ran much better. I can fine tune when I get back home.

                          Rode on a friend's key west one day. My back, neck, and wife are much happier the old Shamrock is back!

                          Comment


                          • #14
                            Set it at 30° total advance.
                            1980 pilot house 351
                            1988 260 predator 408

                            Comment


                            • #15
                              Just a note about timing, 10* btdc is what the spec is for PCM marine engines Ford based.
                              Atlantic City, NJ
                              1982 Cuddy, Rebuilt 351 .060 rings, Edelbrock carb

                              Comment

                              Working...
                              X