DT85 Carb Settings/Tuning

Adam27ktm

Recruit
Joined
Feb 16, 2022
Messages
1
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.
 

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Renan

Recruit
Joined
Mar 27, 2022
Messages
1
hello, in this image that you attached, I see that the screws cover the connectors to synchronize the vacuum are missing, this report of your irregular operation high idle and erase when forcing the engine is a feature of false air inlet install the caps and hoses that interconnect the carburetors that the operation stabilizes
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Welcome to IBoats,

The posted data related to the in-out idle carb turns were excerpted from an Owner's or Service Manual ? With motor Off check if at min throttle if all 3 butterflies remains at same closed position, check same when at max throttle if all 3 butterflies remains widely opened at 180 deg.

Not an issue to check all 3 carbs performance with motor On with a Pro Carb Tune meter before setting the idle rpm right, those carbs have special built orifices in which can connect a hose on each for a perfect trio synchronization. Would suggest to install new spark plugs to deal better with a motor that has been brought back to life after sitting for years ?

Happy Boating
 
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