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1991 Prostar 190 351 surging between idle and 2000 rpm

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  • 1991 Prostar 190 351 surging between idle and 2000 rpm

    Having my first issue with my new to me last year and 60 trouble free running hours ago 1991 Prostar 190 351. Have loved this boat since I got it at 860 hrs and have done lots of the usual maintenance that one wants to do on an old boat. Yesterday I developed an issue after setting out for the day....topped up with 13 gallons of ethanol-free 91 at a reputable Exxon on the way to the lake. Put boat in water, starts normal, runs normal. Several wide open runs and hole shots on glassy morning water and all is good. Temp and oil pressure guages read as usual. Boat sat for about an hour then went out with first skier of the day. Setting out from the dock, starts and idles normal but upon initial acceleration I noticed something not quite right immediately....stumbling/surging power between idle speed and 2000 rpm. Above 2000 rpm engine runs fine all the way to full speed, but immediately powering down to 2000 rpm or below, stumbling/surging happens again.

    So, with a full day of watersports planned, tried to assess the issue on the water (the dock space was not available anymore)....fearing I got some bad gas, I had some Seafoam available and poured a couple of bottles in the tank (tank was full with 30 gallons). Also changed out the cap and rotor to new ones I had on board. After running for a 20 minute to a half hour no change. Pulled the boat out of the water and brought it home.

    After some research on this site, it still seems to be fuel related, however the opposite of what others have experienced (boat starts and idles fine and runs great above 2000 rpm.) I visually tested the Accelerator Pump and seems to be squirting as prescribed. I only have one fuel filter, on the front passenger side of the motor, so I'm going to change that and see if maybe there was some water in it somehow. Looking for some other things to check out over the weekend on my own before getting some professional assistance.

    Recent maintenance: New plugs, Cap, Rotor, fuel filter during winterization, new impeller at start of this season, cleaned the flame arrestor and carb when winterized last fall....and some other stuff I can't recall at the moment. Planning on keeping this for awhile so planning on replacing the fuel line, get some new plug wires, etc. If anyone has any ideas before I go pulling the carb off, please chime in....thanks!

  • #2
    do this

    I would check the carb needle and seat valve. Does the problem get worse after you run the boat for 20-30 minutes? Then the next day when the engine is cold the issue is gone until the engine warms back up? Good luck and keep us posted.

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    • #3
      test the vacuum secondary
      1981 MasterCraft
      19' Skier 351W PowerSlot
      Long gone is the Trans AM waiting for another

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      • #4
        Originally posted by SuperSquid View Post
        I would check the carb needle and seat valve. Does the problem get worse after you run the boat for 20-30 minutes? Then the next day when the engine is cold the issue is gone until the engine warms back up? Good luck and keep us posted.
        I have not been back on the water with it since I pulled it. It did not get any worse after running it the 20-30 minutes after the Seafoam treatment. I was afraid of doing some damage to the motor at that point so wanted to get it off the water to diagnose. Going to swap out the fuel filter and check the gas for contamination first, then go through the carb suggestions. Hope to maybe get it on the water tomorrow morning for a warm up test as you suggested.

        Thanks for the help!

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        • #5
          Pulled the fuel filter and filter is clean and no water to speak of....replaced with new anyway.

          Put the Vacuum Secondaries through their range of motion and although they opened, there seemed to be a bit of resistance through the range....wasn't smooth operation. Before I take it to the lake tomorrow am, going to run it in the driveway and test for vacuum leaks around the gaskets. Then take a look at the Vacuum Secondaries on the water, as what I've seen you need full load for them to work properly.

          Question though, seems the secondaries only engage under heavy load....my issues arise with very little throttle from idle all the way to 2000 rpm. Then when I would think the secondaries would engage, it runs great. Maybe I'm missing something in how they operate?

          Any other thoughts at this point? Thanks!

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          • #6
            Originally posted by quattrotto View Post
            Question though, seems the secondaries only engage under heavy load....my issues arise with very little throttle from idle all the way to 2000 rpm. Then when I would think the secondaries would engage, it runs great. Maybe I'm missing something in how they operate?

            Any other thoughts at this point? Thanks!
            Normal operation for the secondaries. They don't open until a higher RPM. Nothing like running up the river and gouging on the throttle to hear the secondaries open and redline the tach....

            My suggestion is a new carburetor. In particular if that is an OEM carb or by chance a Holley 4010 carb. You will fair very well with the marine Holley 4160 600 cfm.

            I found one last September at Discount Inboard Marine for under $600 shipping and tax (for TN) included using their 10% discount code "USA."

            Make sure you have a good coil and a good EI module. They both can deteriorate over the course of time and heat.

            Check the proper operation and setting of the electric choke.

            Monitor the engine temperature as well. If it is running a little hot, that is another point of consideration for an easy (and unexpected) fix. Poor exhaust hoses (internal collapse) will affect the performance as well, all unsuspecting until complete failure (internally).

            .

            .
            Attached Files
            Last edited by waterlogged882; 07-13-2019, 08:05 PM.
            93 190
            (safe click)

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            • #7
              You have done everything right so far but mention your timing and ignition type. Points or electronic ignition? What is your timing set at?

              I'm going to guess that you have points that are completely worn out. If so, replace them ans set with a dwell meter.

              One note about a new carb.....it will come with the wrong accelerator pump nozzle, wrong accelerator pump cam, and wrong secondary diaphragm spring for your application.
              CUSTOM WHEEL & TIRE PACKAGES
              sigpic

              CUSTOM DECALS - EMAIL FOR MORE INFO

              $125 LED TRAILER LIGHT PACKAGE - FREE SHIPPING
              REBUILDING HOLLEY MARINE CARBS - $350 DELIVERED
              REBUILT COMPLETE MARINE HOLLEY 4160 CARBS $549 DELIVERED
              Email - [email protected]

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              • #8
                Originally posted by thatsmrmastercraft View Post
                You have done everything right so far but mention your timing and ignition type. Points or electronic ignition? What is your timing set at?

                I'm going to guess that you have points that are completely worn out. If so, replace them ans set with a dwell meter.

                One note about a new carb.....it will come with the wrong accelerator pump nozzle, wrong accelerator pump cam, and wrong secondary diaphragm spring for your application.
                Fortunately, Discount Inboard sent the new one to me with all of the correct parts installed.

                The odd parts are typically installed when bought from an auto supplier such as Summit Racing or Jegs, etc....or so that has been my experience...but you have a valid point regardless.

                I think the 1991 model came with OEM electronic ignition. I could be wrong....

                .
                93 190
                (safe click)

                Comment


                • #9
                  Originally posted by thatsmrmastercraft View Post
                  You have done everything right so far but mention your timing and ignition type. Points or electronic ignition? What is your timing set at?

                  I'm going to guess that you have points that are completely worn out. If so, replace them ans set with a dwell meter.

                  One note about a new carb.....it will come with the wrong accelerator pump nozzle, wrong accelerator pump cam, and wrong secondary diaphragm spring for your application.
                  Do you install the #28 nozzle, the 31, or 37, etc...? And the cam color??

                  .
                  93 190
                  (safe click)

                  Comment


                  • #10
                    Originally posted by waterlogged882 View Post
                    Do you install the #28 nozzle, the 31, or 37, etc...? And the cam color??



                    .


                    Purple spring, white cam, #25 nozzle, 5.0 power valve, and #66 jets.

                    Forgot to mention power valve and jets are usually wrong. Most of these carbs are set too rich.


                    Sent from my iPhone using Tapatalk
                    CUSTOM WHEEL & TIRE PACKAGES
                    sigpic

                    CUSTOM DECALS - EMAIL FOR MORE INFO

                    $125 LED TRAILER LIGHT PACKAGE - FREE SHIPPING
                    REBUILDING HOLLEY MARINE CARBS - $350 DELIVERED
                    REBUILT COMPLETE MARINE HOLLEY 4160 CARBS $549 DELIVERED
                    Email - [email protected]

                    Comment


                    • #11
                      Thanks for the replies, guys....my fault for not letting you know what carb I've got:

                      Holley 4160, around 2-3 years old. Has started and run great since I purchased the boat last August and 50-60 hours on it since. It has electronic ignition, a Pertronix FlameThrower 2 0.6 ohm (I have not changed the coil or messed with it at all) and I have not checked the timing yet (don't have a timing light.)

                      Temps have been consistent once warmed up between 140 and 160 ever since I bought it. Temps were within that range with this situation happening as well.

                      Having read a bunch of threads on this forum, the 4160 has solved a lot of peoples problems. I've already got that carb so hoping it's something I can just work out with this one. What typically wears first on these 4160's so maybe I can follow that path?

                      Going to test for vacuum leaks at the gaskets in the morning in the driveway, and get a visual check of the coil and ignition. Then maybe get on the lake for another test session and see if it is temp related or not. Thanks!
                      Last edited by quattrotto; 07-13-2019, 10:59 PM.

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                      • #12
                        Update....

                        Spent some time in the driveway today.....all below performed after engine warmed up between 140-160 degrees....

                        Checked all spark wires with an in-line spark tester, all good even spark.

                        Checked for vacuum leaks around the carb with carb cleaner, no increase in rpms anywhere.

                        Checked the timing and found it was set around 22-24 degrees in advance. I backed it down to 10 degrees advance and it doesn't like that at idle....brings rpm's down too low and it sputters then dies. Will start right back up sometimes with a little gas, other times gas is not needed.

                        Opened up the distributor and cleaned up the (rusty) springs, around the magnets and just made sure things can move freely in there.

                        Timing seems to advance fine, as from idle at 10 degrees, it advances to close to 20 degrees at around 2000 rpms.....

                        So, before I start messing around with the carb settings, what have I discovered and what to do next? Thanks!

                        Comment


                        • #13
                          Sounds like you have chased the carb and fuel system.
                          I had a very similar issue to what you describe. Went through the same process and swapped out the carb, got it running dynamite but had reoccurring problems with the motor cutting out or dropping power after about an 30-60 min of run time.
                          Turns out my coil was getting super hot (I put my hand on the coil when checking the carb). Once the coil cooled down, everything ran great. Swapped out the coil and put a Pertronix unit in it and have since had 5+ years of trouble free boating.
                          Just something to consider. Not always a fuel issue, even though it may feel like one.
                          You have the same coil and spark unit I have. Do you have the solid (epoxy) or oil filled coil? How old is it?

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                          • #14
                            Just bought the boat last August, so I have no idea how old the coil is. The original issue I had manifested itself after a lengthy cool down, so doubting the overheated coil but anything is possible. Gradually replacing components as a preventative measure anyway, so am looking at a new coil regardless. I believe the one I have on there is the epoxy-filled unit, and what I will buy to replace it.

                            Going out to tune the carb now....haven't touched it since I bought the boat so now that the timing is where it should be, need to bring the carb to baseline spec. Wish me luck!

                            Comment


                            • #15
                              Originally posted by quattrotto View Post
                              So, before I start messing around with the carb settings, what have I discovered and what to do next? Thanks!
                              I would again inspect that advance. You seem to have located a problem in that you were set to idle at 22 degrees advance and it didn't idle well at 10, then you found an issue with the mechanical advance that when addressed seemed to allow the engine timing to be set to 10 degrees? Or it then wouldn't idle at 10 degrees after cleaning the advance?

                              What is total advance that you are getting at 4k rpm?

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