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DF15 wrong carb?

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  • #16
    Thank you Jim and Art. I did follow up on your suggestions. First - I know there is a mixture adjustment under an anti-tamper (Welsh) plug nut I believe that is only 'idle' mixture and the motor idles good and does not hesitate so I didn't drill out the plug. Re the carb part number, I can't find a part number anywhere on the carb. It just says 'Suzuki Japan' and the part number on the box is the right part number. But who knows if the carb that came is the box belongs to that box.
    Prop size - I ordered an 8 pitch prop, down from the 10 that is currently on it. I'll try that before taking the carb apart.
    Re the linkage - there is a boss on the carb that stops the butterfly from opening beyond full throttle and I verified that the shaft is contacting the boss at WOT.

    I'm trying to borrow a timing light. I understand that timing is electronically controlled by the CDI and that may have failed.

    Lastly, I'm looking at the depth of the prop. The anti-cav plate (I know that's not what it's called but I've calling it that all my life) is just below the bottom of my hull which is about 6" in under the surface when running on plane. Is that too deep? Would one of those fins on the plate help?
    Thanx again guys


    • #17
      Engine sounds like its set far too deep. Maybe in the process of removing the motor from the boat to work on it, if that happened, and puttingnit back on, it went on too low. Many people with smaller motors set them so the clamp sits hard down on the top of the transom thinking that this is how they have to go, but not the case.

      That anti-ventilation plate (the large one immediately above the prop) should be close to or just skimming the surface when planing along at cruise speed, thats how we try to set them on larger motors and I dont think the smaller ones would be any different. (See the sticky thread at the top of this forum on props and engine height for more info)

      So I would suggest lifting the motor higher on the transom first before changing the prop or doing anything else. Likely to pick up quite a bit of revs and performance by lifting it to the correct height, and its so quick and easy to lift a small motor like a 15.
      Last edited by Moonlighter; 08-29-2018, 07:21 AM.


      • #18
        So I made some careful measurements. The distance between the hull bottom and the motor mount top of the transom is 21". The distance from the anti-vibration (or anti-ventilation) plate to the motor mount top is also 21" give or take about 1/4". So I think we ruled that out.
        In the next couple days I'll check the timing, change the prop and, if it still is not right, try a Doel-Fin. I'll report my progress then.

        Thanx again for all your great suggestions.


        • #19
          I have a question on the CDI maybe someone out there can answer. The spark advance in this motor is apparently controlled by the CDI which has an embeded CPU. The Service Manual simply says to replace the $400+ CDI if the timing is off. When I search Google I mostly get info about Suzuki Motorcycles and they generally say a bad CDI just won't fire. Has anyone ever had a CDI failure that caused, say, ignition timing to be wrong or not advancing with speed? If there no way to mechanically set the initial advance in this motor?


          • #20
            Thought I'd give an update. I put on the new Solas 8 pitch prop. The hardware is very confusing and Solas's documentation is very poor. It appears my old Suzuki prop does not use a thrust washer nor does the Solas, which is contrary to what Solas says. The Suzuki prop had a spacer on the nut side but that spacer won't fit the Solas prop. This info just confused Solas's support guy.

            I installed the Solas prop without either thrust washer or spacer and it fits but the castle nut is at the bottom of the threads and the cotter pin barely touches the castle nut slots. But there is no play and it spins freely.

            Now I'm up to 5100 RPM at WOT with just me in the boat. Still about 800 RPM less than ideal. There is a lot of vibration at WOT. When I spin the prop it doesn't appear to be off but I'll have to check the prop shaft with a dial indicator.

            BTW, Lowes carries non-ethanol gas $20/gal. I must run that through this carb at the end of the season or I will have to rebuild the carb in the spring.

            I'm getting really tired of this motor. I think I'll look for a used Yami.