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NSF-6A temperatures

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  • NSF-6A temperatures

    Have a NSF6A and noticed a couple things while running it today.

    1) While running under various loads up to 1/2 throttle tied to a dock, I was measuring temperatures around the engine with an IR gun. At low speeds everything was around 140 or maybe slightly less), but when I ran up to 1/2 throttle there were areas on the cylinder that were getting to 160F. Is that normal or is it an indication that I'm not cooling sufficiently? The area right around the thermostat was about 140, but the other side of the block was were I see the 160 temps. The impeller is fairly new and there is a really strong pee stream.

    2) I normally have the engine tilt pin in the most forward hole, which means the engine is tilted while just sitting at the dock. When I was idling the motor, I would notice a change in RPM going from about 45 degrees starboard to 45 degrees to port. There would be a 200 RPM drop going to starboard from where the RPM was when pointed to port. I changed the pin so the engine was level and the RPM change went away. I'm assuming this is because of the carb tilts differently when going one way vs the other and that the float bowl gas level changes ever so slightly. Anyone ever notice this? Might this indicate something amiss in the carb? (the carb was brand new ~2 years ago when I changed from a 5hp to 6hp)

  • #2
    I have power trim on my outboard. I can adjust trim from roughly -15 degrees to +45 degrees. Swivel left or right, no change in rpm whatsoever.

    Have you checked fuel pressure?

    How old is your fuel pump?


    • #3
      Those temps sound OK. Different ventilation/cavitation or fuel level in the carb could cause that slight variation. I wouldn't worry about it.
      Certified Tohatsu TLDI Technician
      Buffalo NY USA


      • #4
        Well here's something interesting. Before I saw your replies I thought I'd take the thermostat out and test it. Put it in some 140 degree water and it opened up, but not very far. The spec is only 3mm, so I guess that was close.

        I left it out and went for a run. The pee stream was not as strong (expected that), but I found after I did some high speed running that the engine was up to about 140 anyways, with no thermostat. Hmmmmm. Might I have some other obstruction in there somewhere? I might pull the water pump apart too just to see if there's anything interesting in there.


        • #5
          In the summer, the stat just helps you warm up faster, so nothing unusual there. Pee stream should be similar; the pee tube just shows you are pressurized. If in salt water. might not hurt to see if salt away helps with corrosion.

          Is there any actual problem here, or just curiosity?
          Certified Tohatsu TLDI Technician
          Buffalo NY USA


          • #6
            Sorry for the delay in the reply.. I wanted to check a couple things and retest. This is a long post, but I'm trying to capture all the known data.

            Yes, there is an ongoing issue and I thought/think it might be heat related.

            This issue has been going on for over a year. While you could describe it as "intermittent", it is very predictable so I hesitate to use that word. The engine will run fine for a while but then start to sputter and try to stall. I might be able to save the stall by getting out of gear and modulating the throttle, but sometimes that doesn't work.

            It is very predictable in that it will run 100% fine at startup but then depending on how much a load, it will start having problems. The most common occurrence will be starting from cold, idling out to the lake (freshwater), then getting up on plane. After almost exactly 3 miles of high speed operation (>75% throttle) the engine will start to miss and lose power, as if running out of gas. The other repeatable occurrence is if you run the engine at lower speeds for over an hour straight. When the issue has occurred, if you stop for ~15 minutes, either remove the hood or leave it on, then you can restart and everything will be fine for a while - but not as long as it took for the initial symptom to occur. If you try and restart right away, you may have a hard time restarting but the symptoms will recur shortly afterwards.

            If I run for 2 miles, stop and rest then I can run 2 miles back unimpeded. If I go 3 miles, it starts to lose power and will likely stall. If I just try and restart and head back it will periodically lose power and stall and I'll have to restart probably 10 times to get back. If I wait ~15-20 minutes after the first loss of power, then I can probably make the return unimpeded.

            The primer bulb can be pumped but it does not affect the symptoms. You can duplicate the issue on two different external tanks or using the internal tank. It is not a tank vacuum/vent issue, nor a fuel quality issue.

            If the engine stalled and you try and restart right away, it will likely not restart immediately, however sometimes the oil pressure indicator will blink repeatedly while pull starting. Normally this light might only blink at the start of the first pull, if at all. When the symptoms are occurring, you can pull 5-10 times and the light will blink. I have disconnected the oil switch to see if that was faulty and there is no difference in the symptoms. I did not actually measure oil pressure, but ruled out that or the switch when I disconnected it. The oil light does not blink or turn on when the engine is losing power, only during SOME of these restarts, if you try and restart shortly after it stalled. I also disconnected the kill switch to make sure that didn't have some kind of issue and it does not affect the symptoms.

            I've checked valve adjustment (twice) thinking that perhaps when the cylinder and valves get hot from extended operation they might be too tight, but that was not the case (I did run them with excess play once just to check).

            The last couple times I noticed the problem I had a cheap digital tach connected and it started dropping RPM quickly as the engine was losing power. To me that says it's clearly an ignition issue.

            I have replaced the CDI module twice - once with a used one and once with a brand new one (I got the new one from you, Paul)

            I have also replaced the spark plug (twice) and trigger/timing coil but not the charge coil or ignition coil. All of them pass the resistance tests in the service manual. I think I'm going to try and duplicate the resistance tests while heating the ignition coil to see if that might have an impact.

            ANYTHING ELSE I"M MISSING? It's funny that the engine is actually very reliable if you work around these patterns. I would not be concerned taking the engine across a 25 mile lake because I know it will work, it just might have a sit for a little bit in between periods of running.


            • #7
              Hmm. Could be a thermal electrical problem. In addition to the CD, there is the exciter coil and the pulser coil, as well as the ignition coil. Any one of those could be acting up when hot, then working OK when cool. The exciter charges the CD, and the pulser tells it when to fire.

              On the newer units, all that is integrated into an ignitor module, and there isn't any separate CD.

              The oil light will trigger when the CD fires but oil pressure is below about 4 psi, so that's normal. Plus it indicates that the CD is powering up. If I were to just guess, I would try swapping the ignition coil; it's fairly easy to swap, moderate cost, and since you do get the LED, odds are the exciter and pulser are operating OK.
              3H6060500M IGNITION COIL $43.88
              Certified Tohatsu TLDI Technician
              Buffalo NY USA


              • #8
                Well, I did a little experiment with the ignition coil. I cut a block of aluminum and clamped it to the coil with some heat sink compound and went and ran the motor. Thinking that it would suck heat away from the coil and allow it to last longer if it was a coil-heat-related issue. Ran the motor and only got about 1/2 as far as normal. When I popped the hood I noticed that the block of aluminum was actually pretty warm. Thinking that maybe it was helping heat the coil and it was a coil-heat-related issue, I went and got a coil from our local dealer and put it on.

                Still have the same problem!! ARRGH!! Time to start over.

                It's getting late in the season though, so not as many people are hanging out in the marina. I may be able to start running it at the dock instead of taking out on the lake for troubleshooting. That would help.


                • #9
                  Try the exciter coil. That could be it.
                  Certified Tohatsu TLDI Technician
                  Buffalo NY USA


                  • #10
                    Well, resurrecting this thread from last year. Still have the same problem.

                    I hooked it up to a scope this year and can see very large (+/- 160v) pulses coming from the exciter, and regular pulses from the pulsar coil. I get a VERY weak spark when it's "working" which explains why starting it is much harder than it was before. The exciter coil reads about 95 Ohms in resistance and doesn't show any shorts to ground. I've come to the conclusion that all three of the CDI modules I have are defective with the same issue.... which is probably why they only used those on the 'A" variants of these motors.

                    I'm debating now just parting out the motor or doing a custom CDI.


                    • #11
                      What are the ignition coil resistance readings again? Could be just a weak coil, or one that overheats and fails.
                      Certified Tohatsu TLDI Technician
                      Buffalo NY USA


                      • #12
                        I replaced the ignition coil last year. In previous threads I also replaced the spark plug (twice), the pulsar coil and the CDI (twice). Symptoms would change a little bit but nothing solved the problem.

                        Today I re-did all the readings with two different meters (both digital though).

                        Ignition coil primary (manual says "0.02-0.38 Ohm")
                        Old coil 0.2
                        New coil: 0.1

                        Ignition coil secondary (manual says "3,000-4,000 Ohm")
                        Old coil 11.2k
                        New coil: 10.7K

                        Exciter (manual says "119 Ohms +/- 20%")

                        Pulsar Coil (manual says "186 Ohms +/- 20%")
                        Old Pulsar 191
                        New Pulsar 192

                        I cannot find the specs for actual voltage readings for the different coils using a DVA. I thought for sure I had this somewhere but I can't seem to find it now. Perhaps I had it in a bookmark somewhere. Do you have these? I have a good oscilloscope to get good measurements, just unsure what the exact numbers I'm shooting for.

                        Maybe there's hope. I ran across two old threads, one from 2011 and one from 2016, where they eventually replaced the charge coil. One guy was having the same "weak spark" symptom and said his charge coil "was out of spec for ohms and volts" but doesn't give the actual measurements he had. His ignition coil also read much higher than spec but he also had one from a working motor to swap in to rule that out.

                        I think (and hope) your suggestion from last September must be it. It's the only thing I haven't changed yet. I have an exciter coil on the way. Hopefully that's it, but it's hard to understand that failure as it's a pretty simple coil... just a section of wire wrapped around a core, with no apparent shorts or opens. Wondering how it could really go "bad" and just be enough out of spec that it makes things not work. If the new one works I may be doing an autopsy on the old one to find out.


                        • #13
                          Any coil can fail thermally, and be OK when cool. The issue is you have to have it failing when you take readings, in order to see anything wrong.
                          Certified Tohatsu TLDI Technician
                          Buffalo NY USA


                          • #14
                            Originally posted by pvanv View Post
                            Any coil can fail thermally, and be OK when cool. The issue is you have to have it failing when you take readings, in order to see anything wrong.
                            Yep, those symptoms are the hardest to troubleshoot on time. Does that model counts with a Temp Sensor ? Is all the fuel related circuit tank to carb immaculate clean ?

                            Happy Boating

                            Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers


                            • #15
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                              Here's the thing... for the last couple years it has never run "right" but also has this intermittent issue where it quits and you can't restart for 5 to 10 minutes. It used to be VERY easy to start, often on the first pull. For the last couple years you'd have to get the choke procedure JUST RIGHT or it would be very hard starting and stall frequently.

                              So I did get the new exciter in. Can't wait to take it back out onto the lake, but there is already a significant difference in the measurements. The old exciter was within specs, but just barely. (it was right at 20% tolerance to spec).

                              Here's some oscilloscope measurements of the exciter voltage under load, as it was connected to the CDI and generating spark. I was also able to capture the actual spark and you can see how weak it is on the left and how strong on the right.

                              Click image for larger version

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