Home Forum Ask A Member 1974 Evinrude 9.9 won’t idle at low RPMs, need help

Viewing 10 posts - 11 through 20 (of 57 total)
  • Author
    Posts
  • #35395
    hotpickle
    Participant
      quote FrankR:

      My 1st guess is that the high speed orifice (jet) is partially clogged. That would account for the excessive choking need. 2nd guess (well actually 1st) is have you heard yet that those motors were notorious for fouling spark plugs? Are you sure it is running on both cylinders? Try new plugs, I don’t care if they were just put in recently. I’ve seen brand new motors that wouldn’t run one weekend without fouling plugs. Bad.

      3rd guess is major air leak. But let’s not go there yet.

      The high speed jet is clean, i didnt have to get anything out of there. I snaked through with a wire and checked it.

      I did have black sooty residue on the spark plugs, one had more than the other. I have read thats a sign of a heat range that is too cold?

      #35396
      PugetSoundBoater
      Participant

        I’ve used NGK BR7HS ,part#1098. Gap at .030. A bit hotter than what you have.

        "Some people want to know how a watch works, others just want to know what time it is"
        Robbie Robertson

        #35399
        frankr
        Participant

          US Member
          quote Hotpickle:

          quote FrankR:

          My 1st guess is that the high speed orifice (jet) is partially clogged. That would account for the excessive choking need. 2nd guess (well actually 1st) is have you heard yet that those motors were notorious for fouling spark plugs? Are you sure it is running on both cylinders? Try new plugs, I don’t care if they were just put in recently. I’ve seen brand new motors that wouldn’t run one weekend without fouling plugs. Bad.

          3rd guess is major air leak. But let’s not go there yet.

          The high speed jet is clean, i didnt have to get anything out of there. I snaked through with a wire and checked it.

          I did have black sooty residue on the spark plugs, one had more than the other. I have read thats a sign of a heat range that is too cold?

          Possibly too cold, more likely just the old fouling problem rearing it’s ugly head. But we can’t automatically jump to conclusions, it could be too rich (other one lean) etc. Hotter plugs may help burn the crud off. Try ’em.

          #35400
          fleetwin
          Participant

            US Member - 2 Years

            Well, this particular engine might be in pristine physical condition due to lack of use because it has been a problem child since new. The 74-76 9.9-15s were not OMC’s best efforts and had several update kits to improve running problems. All that being said, I don’t want to just condemn your engine because it is a 74-76 9.9hp.
            Like everyone says, start with simple stuff. Compression, spark, etc…. The engine sounds like it is running on two cylinders, just dying out due to lack of fuel, but start with new plugs gapped at .030". The last time I knew, these engines used Champion UL-81J spark plugs, I have never tried the NGKs, but guys swear by them. Perhaps the fuel pump is weak, or there is an air leak in the inlet side of the fuel system. You mention using an old tank that appears to be unvented. Pump the fuel bulb up hard before starting the engine, then have an assistant pump the fuel bulb while it is running. A fuel supply problem is indicated if the idle improves using this method. Please do not attempt to rebuild this fuel pump, there are many tiny pieces that are tough to reassemble properly.
            This could be a carb synchronization problem, a throttle plate that is not closing properly/improperly adjusted/partially stuck open would cause the exact running symptom you are experiencing. These early engines had some funky lockout linkages that were connected to the throttle butterfly, I have seen many that were stiff causing the throttle plate not to close fully. Someone may have messed with the synchronization and messed it up as well, causing the throttle plate to be held partially open at idle.
            You have had this carb apart, and it looked clean inside. Generally speaking, these are pretty rugged/simple carbs, but it surely is possible to have a plugged idle passage that can only be investigated by removing the welch plug. This is not a difficult operation, but the mixing pocket is very shallow, so extreme care must be used when drilling through the plug. The simplest way to rule out carb problems is by just trying out a different carb on the engine, but I am assuming you don’t have access to another carburetor.
            You may have an intake manifold problem, bad gaskets, or broken/bent reed valves. Does it look like the intake manifold has been off before, do the bolts look tampered with? I don’t recall upper/lower seals being a big issue with these engines, but anything is possible. But, like Casey says, you would probably see evidence of oil drooling down under the mag plate if there was a problem.
            You mention that you just bought this engine, so I am assuming it has never run properly for you, is that correct? Did you get any service history when you bought it?
            Remember, stick to the simple stuff, most problems are simple until we confuse things by digging into bigger issues and creating more confusion. You have picked a real challenge for your first project!

            #35407
            frankr
            Participant

              US Member

              The UL-81J is a booster gap plug. That is, the spark jumps a gap within the plug before getting to and jumping the gap at the tip. That forces the voltage up, which helps it to fire a fouled plug. I’m not familiar with the NKG’s, so not going to make a comment or choice there. Matter of fact, I don’t have up-to-date experience on those engines at all. Other guys here do. But an awful lot of these grey hairs were gotten while trying to make them run back in "the day".

              #35409
              PugetSoundBoater
              Participant
                quote FrankR:

                The UL-81J is a booster gap plug. That is, the spark jumps a gap within the plug before getting to and jumping the gap at the tip. That forces the voltage up, which helps it to fire a fouled plug. I’m not familiar with the NKG’s, so not going to make a comment or choice there. Matter of fact, I don’t have up-to-date experience on those engines at all. Other guys here do. But an awful lot of these grey hairs were gotten while trying to make them run back in “the day”.

                Thanks for clairifying the specifics on the Champ UL81J, I will try both those and NGK

                "Some people want to know how a watch works, others just want to know what time it is"
                Robbie Robertson

                #35411
                hotpickle
                Participant
                  quote fleetwin:

                  Pump the fuel bulb up hard before starting the engine, then have an assistant pump the fuel bulb while it is running. A fuel supply problem is indicated if the idle improves using this method. Please do not attempt to rebuild this fuel pump, there are many tiny pieces that are tough to reassemble properly.
                  This could be a carb synchronization problem, a throttle plate that is not closing properly/improperly adjusted/partially stuck open would cause the exact running symptom you are experiencing. These early engines had some funky lockout linkages that were connected to the throttle butterfly, I have seen many that were stiff causing the throttle plate not to close fully. Someone may have messed with the synchronization and messed it up as well, causing the throttle plate to be held partially open at idle.
                  You have had this carb apart, and it looked clean inside. Generally speaking, these are pretty rugged/simple carbs, but it surely is possible to have a plugged idle passage that can only be investigated by removing the welch plug. This is not a difficult operation, but the mixing pocket is very shallow, so extreme care must be used when drilling through the plug. The simplest way to rule out carb problems is by just trying out a different carb on the engine, but I am assuming you don’t have access to another carburetor.
                  You may have an intake manifold problem, bad gaskets, or broken/bent reed valves. Does it look like the intake manifold has been off before, do the bolts look tampered with? I don’t recall upper/lower seals being a big issue with these engines, but anything is possible. But, like Casey says, you would probably see evidence of oil drooling down under the mag plate if there was a problem.
                  You mention that you just bought this engine, so I am assuming it has never run properly for you, is that correct? Did you get any service history when you bought it?
                  Remember, stick to the simple stuff, most problems are simple until we confuse things by digging into bigger issues and creating more confusion. You have picked a real challenge for your first project!

                  No it has never ran properly for me. It’s just been a series of trial and error (lots of error). I was not given a service history, the guy just said he doesn’t want to tinker.

                  The bro in law showed me the fuel pump trick (he has been a huge help with everything so far as well). It didn’t change the condition. He actually has a ’75, I might be able to try out a different carb actually.

                  There are no signs of tampering, structural damage, or bent reed valves. When you talk about the carb synch, when you refer to the throttle plate, is that the reed valve that is at the back? Not the one that is the choke. If so, that was flush. Is that controlled by the cam follower? As for the carb synch, do you have any links where I can read more about that? I actually thought about that when I was working on it, but I didn’t take good enough pictures. I guess the best way I could describe it, is that it seemed like the throttle was restricted. The cam follower barely moves.

                  #35414
                  fleetwin
                  Participant

                    US Member - 2 Years

                    Well, borrowing your brother’s carburetor would answer a lot of questions quickly! Changing the carb is kind of a pain, cuz you need to move the manual starter out of the way to get at one of the carb retaining nuts. Once the manual starter is loose, thread a 3/8 wingnut onto the thru bolt to hold everything together. Do not pull the thru bolt all the way out of that starter, there is a spacer/washer inside that you don’t want to dislocate. Be sure to get the starter cup locating tab back into its hole on the manifold during reinstallation as well.
                    And yes, there isn’t much movement in that mag plate when in neutral. But, there is an adjustment on the shift lever cam that will allow you to raise the neutral speed limit on this engine. Look on the right side of the engine where the shift lever connects to the shift detent cam, you will see the limit/stop that is retained with two screws. Simply loosen the two screws and move the stop forward to increase the neutral speed limit.
                    The throttle cam/carb sync isn’t too tough to do, I know it would help if I could provide some pictures. The thing to remember here is that the throttle plate on these engines is completely closed when idling. Look on the mag plate throttle cam, you will see a raised mark/arrow. Basically, the carb butterfly/throttle plate should be completely closed until the raised mark/arrow is in the middle of the carb throttle plate roller pick up. Unfortunately, the adjustment on this engine isn’t too easy because one of the cam retaining screws is sandwiched between the flywheel and mag plate! A quick test is to look at the throttle roller while the throttle is in its idle position, the mag plate throttle cam should not be touching the throttle roller. Slowly advance the throttle, the carb butterfly should just start to open when the raise cam mark is in the middle of the carb butterfly roller. Don’t get worried if the throttle plate starts to open only after the mark passed the middle of the roller, this will only cause a rough/rich off idle situation, which is not what you have going on. A carb butterfly that opens too early, or is still partially open at idle will spit/stall like your engine does. Keep in mind that just because the roller is not touching the cam does NOT guarantee the throttle plate is completely closed. A weak butterfly spring, or worn throttle plate could hold it open slightly. Your engine also has a recoil lock out that is connected the throttle plate roller linkage, this could cause the butterfly to be held open as well if things are stiff. Unfortunately, the only way to ensure the butterfly is closing completely at idle is to remove the carb and look at throttle plate movement from the back of the carb.
                    There is no way of telling whether the reed valves are broken/not seating properly unless you remove the intake manifold, let’s leave this for a later step if your brother’s carb doesn’t improve things and you don’t find sync/linkage problems.

                    #35415
                    garry-in-michigan
                    Participant

                      Lifetime Member

                      It will foul plugs if the thermostat sticks open and the engine runs too cold. This can happen if the water pump fails and the thermostat gets hot enough to blow out the expansion jell that it uses to regulate the opening. It should normally run around 145 degrees Fahrenheit. The thermostat used opens around 140 …

                      #35418
                      fleetwin
                      Participant

                        US Member - 2 Years
                        quote Garry in Tampa:

                        It will foul plugs if the thermostat sticks open and the engine runs too cold. This can happen if the water pump fails and the thermostat gets hot enough to blow out the expansion jell that it uses to regulate the opening. It should normally run around 145 degrees Fahrenheit. The thermostat used opens around 140 …

                        Garry makes an excellent point! Once again, don’t skip over the basics, simple stuff!

                      Viewing 10 posts - 11 through 20 (of 57 total)
                      • You must be logged in to reply to this topic.