1993 Suzuki DT25c Idle Issue

[shooter5635]

Hey all, I've got a 1993 DT25C. I've got the factory service manual coming as a christmas present, but I'm hoping y'all can give me some help before that arrives as it is duck season here in Arkansas.

I bought the outboard used. Fresh full rebuild. New rings, pistons, bearings, full machine work, etc. It has maybe 15 hours on it.

I'm having an issue with the idle. For these Mikuni carbs, when you screw out the idle mixture screw, does it lean out the mixture? I synced up the linkages so all three throttle plates are sitting closed together. They were slightly off and I thought that might be my issue. No change. My mixture screws are 4 turns out which seems a bit much to me, from what i've read online. It should be closer to 1.5-2 if what i'm reading is correct. If I screw them in, it starts to sneeze and cough. It idles smoothly around 850rpms in gear with them set at 4 turns. All of this was set with the motor warmed up in the water on the boat off the trailer.

Also, should the throttle plates be completely closed at idle? As in no gap at all? As of right now, they are opened slightly per adjusting with the idle speed screw on the middle carb.

She runs like a race horse. No lag or stumble. Gets up and goes. Plugs looked fine. Nice and brown. Piston color looks good too from what I can see through the spark plug hole in the head. She isnt leaking oil out the prop to suggest running overly rich after idling for awhile like my old johnson would.

It's worth mentioning the motor has some "work" done. Bored pistons. Shaved head. 30 carbs and linkage. Cut tuner. Drilled exhaust. I have a set of Boyesen reeds waiting to go in when I have time as well.

Any suggestions or insight?

[Solarman]

Ok, sounds like the carbs are not getting enough air for the mixture screw to be that far out. Those air pas-sages in each carb have to be blown-out/ clean to breath. All throttle plates closed at idle. Sync all throttle plates to open identically, at the same time. All air mixture screws identically set, generally around .75 to 2.5 turns (the manual will give you the correct setting).
An even light tan/brown color on each plug usually indicates running with proper fuel/oil/air mixture. Also, idle stop screw should be set about 750 - 850 rpms. Again, set by manual. The manual settings are how the motor is setup, with respect to timing.
Make sure you allow a good full 12 hours for breaking motor in, with extra oil in fuel.

Good luck, post back when able, to let us know how it's going, or if something else comes up.

[shooter5635]

What’s the best way to safely remove the throttle position sensor so the carbs can be disassembled and cleaned? I’ve heard they are very, VERY fragile.

[Solarman]

On your model it's fixed position, and just screwed to body of carb. The throttle shaft extends into the TVS, to give position. Just remove screws, slide off shaft.

Some motors/carbs have different size jets between top, middle, and bottom carbs from factory to balance running those motors. Do not mix parts between carbs, or positions of carbs. Take pics before removal, to insure all hoses, and other parts, wires go back where they should.

Do not remove any more than float bowl, float, needle valve & seat, main jet asy, air mixture screw & air jet (top screw on carb). Record what the air mixture setting is before removal if you do not have manual. All multiple carbs air mixture screws are set identically, why manual gives only one setting.

Do not change any linkages, idle stop screw setting, or any other parts of carb to soak/clean.
Always use good compressed air to blow through each small hole in carbs & jets, for air and fuel pas-sages, to clear and dry them out.

Good luck, post back when able to let us know how it's going, and what you find out.