DT85 Carb Tuning

[Adam27ktm]

Got some issues with my DT85 (8501-031174) - any help would be greatly appreciated. A little background.. the boat/motor was given to me after the motor sat for years. It wouldn't start initially - all 3 carbs were gummed up with bad fuel. I took off all 3 carbs and thoroughly cleaned them, and also completely drained the fuel system on the boat and flushed it out. After re-installation, the motor will now run. I put it in the water and ran it for a full hour with no issues.. but when i got back near the dock and started to idle down, is when i started to have issues. The motor didn't want to idle and kept cutting off when put in Forward. After letting the motor cool down, it cranked right back up. My problem is i can't find any information for fine tuning the carbs. Per the manual - it calls for the air pilot screws (red circles in picture) to be fully screwed in, and then backed out 1 1/4 - 1 3/4 turns. I have all 3 of them backed out 1 1/2 turns. The manual calls for idle to be around 1,000 RPMs - but even with the idle adjustment screw (bottom blue circle) backed all the way out, i'm sitting at 1,200-1,500. I'm not worried about it idling a little high, but i'd like to have everything done right before i take it out again. My main question and issue that i have is that I can't find any information on initial settings for the top 2 blue circles in the picture. I'm not even sure what they are, any manual i've found doesn't even mention them. I can adjust either of them in to the point that it will idle down and eventually cut off the motor. When the carbs were removed and cleaned, i counted the turns when taking those screws out and re-installed back to where they were - but i'm not confident they were correct in the first place. I have a carb tune pro to sync the carbs - but didn't want to get into syncing them until i knew that i had those two adjustments set correctly.

[Solarman]

The middle blue appears to be a screw for the back butterflies, not easy to tell from pic, very fuzzy, especially if zoomed in. Back out a little, only far enough to get motor down to about 900 rpms.
Then using the idle stop screw (bottom blue circle) screw in till you get to 1000 rpms. If this is the screw I think?

The air mixture screws should be set identically for all the carbs. Look at the plugs after running a bit (mostly idling), if black you should open all to 1-3/4 turns, to let more air in to mix.
If the plugs are tan/light brown color leaves them alone.
If still bright white they may be burning too lean, turn the screws in 1/4 turn for less air.

The color of the plugs dictates the air mixture setting between the 1-1/4 to 1-3/4 setting. You might have to idle quite a bit to get it just right.

The top blue circle I looked for in parts, don't see anything like it? Im wondering if those carbs are the original carbs?

There does seem to be an air pilot screw on top of all three carbs in the pic for the 2000 year model, these are usually screwed down snug, and are a set metered size. The parts page gives different sizes for different years, and positon of carb.

Good luck, post back on what you find out.

[Adam27ktm]

Thanks for the reply. (I think) the year model of this motor is 1980 from what i found online. Unfortunately, like you said.. i can't find the adjustment screws in any of the parts schematics or workshop manuals that would indicate what they are. Thanks for the advice on the air mixture screws - i'll definitely use that technique to get them adjusted correctly after i get the idle sorted out.

"Then using the idle stop screw (bottom blue circle) screw in till you get to 1000 rpms. If this is the screw I think?"

Yes, the bottom carb on this unit has no individual adjustment, and only has the screw that will adjust the butterfly on all 3 carbs. Only the top 2 have individual adjustments. I'm guessing my best bet is to fiddle with the top 2 adjustments until it's running smooth around 900 RPM's, and then screw in the bottom idle adjustment until it's up around 1,000?

[Solarman]

Apparently you do not have a Suzuki service manual?
Re-read my post. I've tried to describe each screw in the blue circles?
If you see any names and #'s on the carbs, especially the top and middle, post them here. I might be able to look up info on the carbs?
If I search different years, I still show no carbs with those adjustment screws?

post back to let us know what you find out.

[Adam27ktm]

I've tried every manual that i've been able to get my hands on.. Suzuki OEM, clymer, etc..
I have also gone through every dt85 year parts schematics and also cannot find any carbs with the adjustments that mine have. I will check this afternoon and see if i can find any numbers or other info on the carbs and post back here.

[Murray]

Is there a chance the motor was manufactured for a country that doesn’t worry about emissions? I recently learned on this forum that Suzuki still manufacturers 2 stroke outboards, they just don’t sell them in North America due to emission regulations. I’m wondering if you have one of those engines or something along those lines. Just a thought.

[Solarman]

Murray this DT 85 is a 2 stroke. The serial number posted indicates a 2000 year model?

Adam it might help to see a pic of the serial number plate as well.

[Adam27ktm]

So without removing the carbs, the only letters i can see is the manufacturer - which is "Mikuni Corp". All 3 say the same thing. Is that who made the OEM carbs for year 2000?

[Adam27ktm]

Top carburetor

[Adam27ktm]

Middle carburetor

[Adam27ktm]

Bottom carb

[Adam27ktm]

Bottom carb

[Solarman]

Mikuni is a common carb used on many motors. Often they have a number for the carb somewhere on the carb? I'll try to look up mikuni carb and see if I can locate something?

[Adam27ktm]

I was un-able to find any numbers without removing them. I plan to remove them and inspect for numbers one night this week - will post back what i find

[Solarman]

When they are removed, take a few pics of what those 2 screws are connected to. Keep track of the original adjustments for each of those screws. Try to see if they look like they were factory installed? Or maybe if a previous owner might have added them?

Post the pics so we can see what those screws might do.