Stalling engine while in forward gear

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  • jgnobis
    Frequent Contributor
    • Aug 2023
    • 7

    Stalling engine while in forward gear

    Hello all. Spent some time reading through older threads and doing some troubleshooting on my own and I'm trying to narrow down next steps. Here are my symptoms:
    • Engine starts normally, runs normally in idle and doesn't stall in reverse or feathering forward or in forward gear at low idle.
    • As I accelerate, slowly and try to reach higher RPMs, she starts to stall out. If I lower the throttle and take her out of gear, she stays running.
    • Once stalled, she starts right up no problems and usually I can idle forward without stalling, but then as I try to slowly go to higher RPM she'll try to go to higher RPM and start to stall out again.
    • I've been successfully able to idle forward underway (after a couple of stall-outs) for a long time and very, very, very slowly increase throttle over time and if that works for 5+ minutes or so she's usually good to go for the duration of the trip under motor.
    • I've also tried warming up dockside in forward gear at idle or just above idle for 15 minutes (without stalling) before venturing out. Still will stall at higher RPMs.
    Troubleshooting steps I've done:
    Removed, cleaned and reinstalled carb. No noticeable blockages or gunk. Carb was replaced a few years ago.
    Replace fuel filter, checked for water with no apparent water in the line or fuel filter enclosure.
    Played with adjusting air screw on carburetor to ensure idle and air mix is good
    Prop check, not fouled

    Looking for thoughts on next steps to look at:
    Fuel pump?
    Coil?
    Drain and clean all fuel from system?

    Any thoughts or ideas would be greatly appreciated as I don't understand why after very slowly increasing RPMs over time won't it might not stall. Thanks much. John
  • Al Schober
    Afourian MVP
    • Jul 2009
    • 2034

    #2
    John,
    To me it sounds like fuel starvation. How does it respond to a shot of starting ether? Many of us have added a small pressure gauge at the inlet of the carb to help isolate issues with fuel pumps and filters.

    Comment

    • Dave Neptune
      Afourian MVP, Professor Emeritus
      • Jan 2007
      • 5117

      #3
      The stalling you describe does indeed sound like fuel starvation which can be difficult to figure out unless you have a fuel pressure gage in the line as Al described.
      Did the problem manifest slowly as in 4 or 5 uses of the boat or all of a sudden? If cleaning the carb made no difference checking fuel pressure is a must before delving further into minute possibilities.
      A cheap gage is just fine and if you can find one that operates at low pressures all the better. If not any fuel gage will work. You are looking for 2~4 psi to feed the A-4 so the lower range gage is just a bit easier to read. Zero to 15 gages are pretty common and are not expensive. Once mounted leave it there for any future reference for diagnosing problems. Well worth the money!!!!!

      Dave Neptune

      Comment

      • roadnsky
        Afourian MVP
        • Dec 2008
        • 3129

        #4
        Do you know the condition of your exhaust setup?
        A quick check to rule out a clogged exhaust is to disconnect it from the manifold (2 bolts) a few inches and try running up the RPM in gear.
        Warning... it'll be loud and stinky (don't breathe the fumes) so you only want to run it for a short test.

        More about it HERE
        -Jerry

        'Lone Ranger'
        sigpic
        1978 RANGER 30

        Comment

        • Sam
          Afourian MVP
          • Apr 2010
          • 329

          #5
          An ebay purchased stainless steel case liquid filled glass covered 0 to 15psi fuel pressure gauge for $15 to 20 bucks as mentioned will serve you well as mentioned. "taking out of gear and she stays running" ie " no load" kinda also would lead me to check the distributor springs, & advance weights and lube them.

          Comment

          • jgnobis
            Frequent Contributor
            • Aug 2023
            • 7

            #6
            Originally posted by Al Schober View Post
            John,
            To me it sounds like fuel starvation. How does it respond to a shot of starting ether? Many of us have added a small pressure gauge at the inlet of the carb to help isolate issues with fuel pumps and filters.
            Will give this a try while underway but will order a fuel pressure gauge and work to install that.

            Comment

            • jgnobis
              Frequent Contributor
              • Aug 2023
              • 7

              #7
              Originally posted by Sam View Post
              An ebay purchased stainless steel case liquid filled glass covered 0 to 15psi fuel pressure gauge for $15 to 20 bucks as mentioned will serve you well as mentioned. "taking out of gear and she stays running" ie " no load" kinda also would lead me to check the distributor springs, & advance weights and lube them.
              Thanks for the tip on the type of gauge. I will also check the distributor. Thanks much.

              Comment

              • hanleyclifford
                Afourian MVP
                • Mar 2010
                • 7032

                #8
                Before troubleshooting a problem of this type you should ensure the engine is adjusted to specifications - timing advance, distributor dwell, valve lash. A fuel pressure gauge is a fine thing to have but only tells you what is being delivered to the needle and seat. What is delivered to the engine is finally determined by the main jet which on most engines is a constant source of trouble. If it is partially constricted it will perform at low rpms but will fail to deliver enough fuel at higher rpms. An engine that sits all winter not properly winterized or run in the winter is a good candidate for fuel bowl problems. Take the carb off the engine, take it apart and give it a good cleaning.

                Comment

                • Dave Neptune
                  Afourian MVP, Professor Emeritus
                  • Jan 2007
                  • 5117

                  #9
                  In 34 years with the same motor and carb I never had any trouble with the main jet. However over a two week period of testing fuel mixture with the adjustable jet I did have a problem with it leaking.slightly so I started making my own jets and air corrector too. I found the results I sought via a smaller main jet to lean the high end and a smaller air corrector to move from idle to hi-speed circuit sooner which allowed me to really reduce the idle fuel giving the carb a better transition and did lean the whole carb by lowering the float a bit to. I ran that set up for over 25 years and never cleaned the carb because it ran poorly I just wanted to take a look inside a few times I ran good filters and only regular gas from a gas station and almost never a marina. I also used the Indigo prop which freed the engine up to run at higher RPM's and deliver far better economy as well as power when I needed it.

                  Dave Neptune

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