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How to adjust the idle speed DT115

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  • #1

    How to adjust the idle speed DT115

    Hello Forum,

    I'm a first-time boat owner and my name is Shane Roberts and I live in Lincoln, NE Nebraska. No, I'm not a Husker fan so please don't hold what against me.

    I just bought a 1984 Procraft fish and sking with a Suzuki DT115. I was told the motor is 1986 and serial number plate shows two sets of number 11502(black area) and 404966(silver area). I assume that 404966 is the true serial number but wasn't for sure what 11502 stands for? With that being say is this a true a 1984?

    This boat motor looks brand new when you remove the cover and runs perfectly. The problem I have it's 5 mph trolling speed. My Dad has the same boat with a 115 Mercury and it will get down to 2 mph. Plus that's a little to fast when trying to get it on the trailer.

    I ordered a shop manual from Ebay on a CD. Which has supposed to cover 87 thru 2000 but appears to be more like 1987 to 1997.

    I've google the heck out of this and can't find anything about adjusting the idea speed down.

    The manual talks about the "Idle speed adjustment switch" and shows a picture of it right above the CDI unit. I thought this was going to be an easy fixed, till I found out I don't have just a switch.

    The manual shows a picture of the front of the motor with a "learn" and "Rich" which I do have with a black rubber plug. Is this what I'm looking for and if so does that adjust all four Carbs at the same time? Then they start talking about synchronize carburetor Linkage, which I really don't want to get into.

    I should also add my RPM gauge doesn't work and I haven't did any research on that yet.

    I was told this was a one owner who died about 10 years ago and always garaged the boat. A family member bought it and sold it to me....but knows nothing about it.

    Any help is much apprreciated, and I don't want to screw anythig up.

    Shane
    Last edited by akareddog95; 06-30-2015, 09:31 PM.
    Tags: None
  • #2
    Your serial number 11502 - 404966, Indicates it is a 1984 year model.

    First off don't mess with the air mixture screws on front of your carbs. Those that say lean & rich, they're the air mixture screws.
    Your motor should have one screw on the starboard side of the motor. Well try to send a pic to show you (this is an 86, should be just like yours.), but it should be close to the back vertical linkage for the throttle.

    In this parts pic the one idle stop screw you're looking for is #21. This pic isn't real clear and detailed, but notice the spring #22 is on screw #21, it should be on the second (in this pic), or third carb. Now, where that back vertical linkage connects, is the throttle shaft, the front vertical linkage connects to the choke butterfly shaft.

    Once you find the screw put the flush attachment on for water (never turn motor over dry), start motor, turn screw no more than 1/2 turn ccw for now (cw increases idle). Next time in water see if slow enough. Out of water may sound same, but in gear, in water may be totally different.

    Fig. 6 - Carburetor - Suzuki DT 115 Parts Listings - 1986 to 1997

    Hopefully you can see this link.

    Good luck. Let us know what happens.

    Comment

    • #3
      I meant to ask what RPMs your motor idles at?

      It should be idling about 700 - 750 RPMs, neutral, in the water. In gear it is slightly lower. I can't imagine 5-7 mph if in gear idling? And yes, boat size does affect idle speed.

      Post back, would like to find out present RPMs.

      Comment

      • #4
        Thanks for the information. I can't wait to go home and start working on it.

        To answer your second question, I don't know the RPM it's running at, my RPM gauge doesn't work. There isn't much in the service manaul about non-working RPM gauges either. Any help hints on working on that problem?

        Thanks, Shane

        Comment

        • #5
          Try pulling the tach out of its mounting, careful of wires coming off (might take a couple pics before removing to make sure it goes back same way.), once its out, look for a rubber plug. Remove plug, and may be a switch inside, (note its position) should be a couple positions, switch back and forth a couple times, and return it to its original position. Replace plug, check that wires are good (not corroded/ dirty) replace in mounting.

          If still the same problem, your motor may have a bad connection, or may have a sending signal problem. Did you notice if when first turn key to on (before start) does tach move at ask?

          Sometimes the tach (not working) causes idle issues, but not sure on your motor.

          Post back if you can tell anymore info.

          Comment

          • #6
            Ok I'm going to trying to upload some pictures. I don't see the screw and spring you're talking about. The only adjustment is the one I circled in red in the picture below

            [IMG][/IMG]

            This is much like the idle adjustment on my Dads 115 Merc. Shouldn't it be resting on the rubber stop? Looks like it isn't closing all the way and that's the reason for the fast idle?

            [IMG][/IMG]

            I'm assuming this cable is the issue and not letting the rubber stop come to rest in the full closed position. I also assumed the broken wires are supports for strength and actual cable in still working, but maybe bent?

            [IMG][/IMG]

            I will not get a chance to work on the tach till Friday.

            Looks I'm buying a new cable....do think that is my real issue.

            Thanks Again, Shane

            Comment

            • #7
              I think you're right. That cable is shot. I also think that screw is the throttle stop screw for the idle. Check the shift cable also, if damaged coating, it may not be long before it goes too. Make sure you get same, or proper length, it should be labeled at each end of the cable.if it goes under flooring tie/ tape a good pull cord, so you can pull the new cable back in.

              Good luck, post back after replacing the cable(s).

              Comment

              • #8
                Don't have much help for you on the older motors but that engine is in beautiful shape

                Comment

                • #9
                  It is amazing how clean this motor is. It looks like it's only a couple of years old.

                  Comment

                  • #10
                    Here is my latest update. I replace both the throttle and shift cable last week. The new cable solved my high idle speed problem. The old cable wasn't letting the idle stop return all the way back and rest on the rubber stopper.

                    I got the idle speed down from 4.5 to 2.00 mph. I could get it down to 1.75 mph but the engine would stall out sometimes. So I'm going to adjust the idle adjustment screw up a little before I go out next time.

                    I'm still trying to figure out starting the motor when it's cold..... to choke or not to choke. I flooded the motor once last week. I killed my starting battery trying to start the motor and I had to jump start it with my trolling battery. I trolled for 4 hours and was suprised it didn't charge my starting battery at all.

                    Someone told me at the local boat store, that if your RPM gauge isn't working and not charging there is sometime most likely wrong with the motor......but also claimed to know nothing about Suzuki.

                    Once I get the motor running it starts right up ever time. I'll pull the RPM gauge out next weekend like Solarman previous stated and see what happens and give an update.

                    Thanks, Shane

                    Comment

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