Home Forum Ask A Member Backfire/misfire thru carb

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  • #260000
    Beno
    Participant

      ok spring thaw is in route and the 140hp OMC is back on the plate!  I have two nephews interested in Skiing and tubing this July..

      When I  last visited this I had a cooling problem where the 140 would run a little
      hot and my theory is that the exhaust is pushing the cooling water (or at least
      preventing the cooling water from circulating well) so my current idea is to increase the
      pressure of the cooling water somehow..  suggestions?

      Im thinking electric pump inline… There are a number of electric 12 volt diaphragm pumps that I could use to boost the
      pressure but if they pull more electricity than the flywheel can generate then that idea is out.   the one I have on the shelf here is 1.6amps (25watts?)

      .8gpm (which I dont know if that’s accurate under load)

      So I guess the question is I’m on 140 horsepower OMC Evinrude how much electricity
      in Watts or amps does it put out at what RPMs?

       

      • This reply was modified 2 years ago by Beno.
      #260410
      fleetwin
      Participant

        US Member - 2 Years

        I dunno buddy, I don’t think trying to increase the water pressure with an electric pump is something you can do very easily.  Keep in mind that increased water pressure will most likely overcome the bypass valve springs and result in the engine running cold/poorly at low speeds.    There are many passages that can get plugged up, packed with sand/silt easily.  I really think you should sell this thing while you have it running OK.  You will probably end up spending more time fixing/diagnosing it than actually using/enjoying it.  I’m not trying to be rude, just realistic.  Like I have said, these things were not OMC’s finest hour, and never worked all that well even when working “correctly”.   Did you ever add those fittings in the top of the heads, like the original powerhead had?

        #260444
        Beno
        Participant

          That’s a good point I hadn’t thought of that, hmm.

          Couldn’t I just change the carbs out to smaller 115hp carbs? Wouldn’t that reduce the heat&hp?

          Regardless I would never sell something that wasn’t working totally correct..  I’m much more likely to pull the engine and sell it separately (plenty of people interested in a solid running 140 horsepower OMC powerhead) and then convert the boat into some sort of electric boat . Or whatever…

          #260457
          fleetwin
          Participant

            US Member - 2 Years

            OK, I don’t think the smaller carbs are going to reduce the temperatures much.  I remember the picture of your heat gun showing 190 degrees, but where on the engine/exhaust were you measuring the temp?  That thing has many exhaust/water chambers separate from the powerhead, which may be designed to operate at higher temperatures.  To be honest, I never had that much experience with the turbo jets to know the specifics.  But, if the powerhead is truly at 190F, the overheat alarm should be going off at the console.  Does that alarm work?

            Again, did you ever add those nipples/elbows to the top of the heads that were used on the original powerhead?  Or perhpas, you could swap the old heads back in place which are lower compression heads.

            #260494
            Beno
            Participant

              Hmm.. well.. I may try a restrictor plate just to see if lower carb size makes a diff. Easy check.

              I’m pretty sure my brother was shooting the water jacket on the rear cylinders..

              I will check on the alarm function..  I’ve kind of wondered myself whether or not that’s working.. my understanding is that there are two round heat sensors on a v4 that are kind of stuffed into the heads with brown wires maybe ? and what is it that they do they ground out when they reach high temp?  So the buzzer always has 12v to it and the circuit completes if the temp goes high? The.  Beeeeep?

              The boat and then motor both use red plug system and I just plugged it in on engine swap and was thinking that the alarms would all line up and work..

              I haven’t drilled and tapped the top heads yet…  I may still do it . I found some hydrojet heads in New Hampshire.. but they also seem to come with the trailer of boat two engines and large bill…  not sure I wanr to drive for that.

              I’m really kind of interested in what the water flow rate is through the block. I just bought a flow meter online and I’m going to hook it up and see if I can create a graph against the RPM and see if I’m getting a cooling water drop off at higher RPMs

               

               

               

               

               

               

              #260498
              fleetwin
              Participant

                US Member - 2 Years

                Yes, the two cylinder head sensors just complete the ground circuit to the warning horn.  So, if either bank overheats, the alarm should sound.  So, you can check the warning horn function/wiring by disconnecting the tan leads at each sensor, then grounding the tan wiring harness leads, one at a time, with the key on, horn should sound.

                #260582
                Beno
                Participant

                  Okay I hooked up the battery to the boat and I found both Brown terminals and grounded each one of them and each alerts the screamy alarm underneath the dash…   So could both sensors be bad inside? I’ll have to put my remote theremometer on a accessible spot to see.

                  It also appears that my brother is broken the throttle control which I have to fix a couple years ago and OMC has the chintziest connection system I’ve ever seen.. I’m going to modify and upgrade at this time..

                  basically in the pic you’ll see there are two anchor points and plastic combined with aluminum  little half Moon keyed rounded things hold the anchors together and they just fall apart under the stress

                   

                  #260602
                  fleetwin
                  Participant

                    US Member - 2 Years

                    Not likely that both sensors are bad.  On this set up, you could start the engine out of the water without harming it, let it heat up while running slowly, see if the horn sounds once it heats up.  As for that control box, it is one of the junk “fits all” models from OMC.  I’m sure you could find the proper parts to repair it, or perhaps a used box.  Fix this issue though, you sure don’t want the boat running away from you, perhaps hurting someone.

                    PS:  please don’t let it get too hot, you surely don’t want to melt any of the plastic thermostat components or the rubber cooling water deflectors inside the block…  Should only take a few minutes of running it at low RPM to heat it up sufficiently to set off the alarm…

                    • This reply was modified 1 year, 11 months ago by fleetwin.
                    #260702
                    Mumbles
                    Participant

                      ‘On this set up, you could start the engine out of the water without harming it, let it heat up while running slowly, see if the horn sounds once it heats up.’

                       

                      Uh, maybe remove the gearcase first so the water pump housing and impeller don’t melt?

                      #261945
                      Beno
                      Participant

                        The kids need the boat for vacation on Sunday. So I of course did my best to delay until Saturday morning.. .

                        But the secondary cooling output lines are done!. They are tapped and threaded with 1/8NPT.

                        Luckily I had a spare 115 OMC head to look at to guide me to where to drill.

                        This is not an easy undertaking there’s limited clearance and you have to be sure to drill with pretty exacting placement.. because too far and your drill will only go in to the cylinder also it will help to have multiple NPT taps some with better tapers some with less taper.

                        Time for sea trials!

                         

                        • This reply was modified 1 year, 10 months ago by Beno.
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