DT85 Carb Tuning

[Adam27ktm]

Good afternoon, sorry for the delay. I removed both the top, and middle carbs and inspected them for numbers and found nothing. The screws are definitely factory. I did, however send over some pictures to an old co-worker that did some side work on outboard units and he stated that he believed the adjustments were the "low speed adjustments". The picture attached is taken from the cylinder side of the carb, pointed in towards the butterfly. The red arrow is pointing to the hole that the screws are connected with.

[Adam27ktm]

Assuming that both of the adjustments on the top 2 carbs are low speed adjustments.. how do you think the best way to go about tuning them would be? Or mostly, what order to tune them in? I'll list all adjustments on this unit for clarification..

1) top carb low speed adjustment
2) middle carb low speed adjustment
3) bottom carb - single phillips idle adjustment that will affect linkage to all 3 carbs (main idle adjustment)
4) (3) pilot (idle) air screws - 1 on each carb on the intake side - these are currently all set to 1 1/2 turns open

[Solarman]

Adam, if you put air pressure on that hole (red arrow points to) where would the air in that hole come out? Or, if you remove the adjustment screw, and put air pressure where the screw was, where would the air pressure come out? Im guessing the hole with red arrow, but where else does the air come out?

"If" the air pressure only goes to the hole in the throat (red arrow by butterfly) and outside of carb? Possibly side hole by adj screw location? Then that adj screw (only deals with outside air when "butterfly" is fully closed) is more like a fine-tuning adjustment for only the top and middle carbs during idle "only" (when butterfly is closed). This assumes air pressure for "both" top and middle carbs go to the same place with your air pressure test. Because the bottom carb has no adjustment, it would be the first carb for lean, or rich setting for idle-air-mixture setting. The plug's color tell if that cylinder is running too lean/rich.

"If" the air pressure from "your" test goes elsewhere, float chamber (top/middle/bottom)? Somewhere else? Knowing exactly where it goes can help identify what the adjustment is for?

More pics can help, back up an inch or two, I can zoom in.

Post back if you don't understand what I'm trying to explain, or if you don't understand adjustment for lean - too much air, or rich - too little air adjustment?

Good luck, post back on what you find out.

[Adam27ktm]

I understand completely, thanks for the detailed explanation. I have confirmed that when i apply compressed air, the only area it goes into is the throat (red arrow), behind the closed butterfly. That being said - i agree with you that these two adjustments are the fine tuning adjustments for idle only on the top two carbs.

I have not adjusted the air pilot screws on the intake side of the carbs at all - these are all set at 1 1/2 turns open.

Now that we know what the adjustments are, would you have any input on what order to start adjustments? Just a reminder - i have the carb tune pro tool for syncing the carbs when the time comes.

[Solarman]

If you haven't messed with linkages (adjustments) then all three carbs back butterflies (where red arrow is) should all close identically (to idle stop screw), when all are at full throttle, those same butterflies should all be fully open.
The only other thing to sync is idle mixture screws be set identically. If (as you say, they haven't been changed) then go by the color of bottom plug first, after idling a few days of heavy use. If too dark (rich) open bottom air/mixture screw 1/8th turn (no more than 1/4 if black). If light tan, it's good. If too light close the air/mixture 1/8 th. Again, all 3 carbs set the same. Check color of plugs on all cylinders often till just right. If top, or middle cylinders are different colors adjust "red arrow" mixture screws in to darken (richer), and out to lighten (leaner), providing your air pressure test vented by the adjustment screw for those two carbs. If it vented somewhere else show me with a pic.

Good luck, post back on what you find out.

[nedormot]

Solarrman, You are the first to explain this so I understand. I just need a mild clarification. If the bottom plug is black, do I just back that screw back 1/8 turn and leave the others alone, or do I back them all back 1/8 turn so they remain uniform? I'll phrase this another way. Do I make adjustments independently on cylinders considering the color of the plug, or do I make the same adjustments to all (regardless of the plug color) if I adjust one. Thanks a million. I've been struggling with this problem for a while. My wife refuses to boat with me because I become so frustrated.

[Solarman]

Adam/nedormot,
I would adjust all 3 carb air-mixture screws first identically, according to color of plugs, It will take a good bit of running (at idle) to color the plugs.
Hopefully the idle is running at the 975-1000 rpms now.
Yes, I would set all air-mixture screws (intake side) according to bottom carb identically.
Use the extra screws on top/middle carbs as a "balancing" screw, adjusting (from original setting) ONLY if RPM's are still too high, and very slightly adjusting.
These extra 2 screws are located "after" the air/fuel mixture process, and appear to (increase/decrease fuel passing-by the back butterfly) relating to RPM fine-tuning, so adjust these if idle is still too high, with the idle-stop screw (on linkage) at the minimum setting. You can adjust the idle stop screw to raise rpm's if too low, after all the other adjustments, if needed.

If the top 2 plugs are darker, but bottom plug is a good tan, I would turn the 2 balancing screws in slightly, and use idle-stop screw to keep idle rpm's where it should be.

This is a slow process with coloring of plugs. Don't let it consume you.

Whatever you do, don't let it frustrate you. Boating is an enjoyment.

Good luck, post back how it's going. Relax, happy boating.

[nedormot]

Solarman. Thanks again for your help. You are very generous to give me your time and expertise. It is much appreciated. So I went down to the lake today and checked out the plugs , installed new ones, as well as a installing anew gas tank and line with bulb and new connections. It definitely made a difference. I used the idle screw on the linkage to bring the idle up to 800 rpm. I am still not convinced it is fixed completely though. I kept it tethered and shifted it into gear. It still had a tendency to stall in forward, but not right away. That is better. I couldn't put too much gas to it while tied behind my dock mates much more expensive toon as to avoid a possible disaster. Haha. Anyway, the bottom two plugs looked ok, but the top plug is pretty black. I'm going to try to attach pictures of all three. The plugs have been used through about 10 gallons of gas. I made no adjustments yet. I'm wondering if you think I should do a 1/8 turn adjustment to lean or leave it alone.
MpGn7SIeSKCe9iShkavEVg.jpg Top naKQE+fyRru%DbInnTZ5iQ.jpg middle YuI7YuqPTYaOW3h7tuaixA.jpgbottom

[Solarman]

If all three air-mixture screws are set identically, and each of those adjustment screws are not damaged (any damage could cause different metering of air mixture), then I might open (increasing air mixture) the top air-mixture screw 1/16 turn, but no more than 1/8 turn. I might also consider closing the "balancing" screw (reducing air-fuel-mixture slightly) just about 1/16 turn.

I would check plug colors again after another tank of fuel. Also, you should be adding some stabilizer in each tank of fuel. It does help clean large/small passages and protects the fuel from separating.

You mentioned the manual said RPM's should be 1000, but adjusted to 800 RPM's? Is there a reason it's this low?

Good luck, post back to let us know.

[nedormot]

Good morning Solarman, and thanks again. Your advice has been perfect. I thought a slight adjustment to the top pilot air screw might help that cylinder a bit. I regularly run seafoam in my gas. Do you recommend something other than seafoam? I'll probably double check the condition of those adjustment screws at the end of the season when the boat is out of the water. I have shakey hands and would likely drop one in the drink. That is, by the way, the voice of experience. I set the motor at 800 as the manual calls for idle speed to be 650 to 700 with the prop engaged. (I think you may have gotten me mixed up with another guy earlier in this post who was working on a DT85/different year.) 800 got me as close as I could get with a weak tach on the dashboard, tethered to the dock back of another boat, and by myself. I am ordering a new "test" tach today for better accuracy. Finally, I'm not sure what the "balancing" screw is and where it is located. The manual ( 1987 Suzuki D65 2 stroke) makes no mention of it. I'm going to send you a pic of my carbs.
tdwAiftAQ9G4NGg7SdZDOA.jpgFCXlEIZCQVyqJx03wfj2Nw.jpg
See if you can spot it. The manual makes no mention of it. Thanks again, Solarman. My wife thanks you too. You have been a lifesaver. --Tom

[Solarman]

Ok...sorry, yes Tom I was conversing with Adam from an earlier post, and thought you were the same owner using a different name.
This happens when owners use other owners information and add questions for thier problems.

Seafoam is fine, I also thought 1000 RPM'S was too high (800 rpm's sounds fine), and yes again his motor has additional adjustment screws that I called balancing screws, because the manual gives NO info for them.
Your motor as I see from pics doesn't appear to have those screws, so don't worry about them.

If these plug pics are your motor Tom, I would do the same with the top carb air-mixture screw, just a slight 1/16 turn open.

Good luck Tom, please start your own thread for your own motor info, as it can get very confusing to get things straight.

Good luck.

[nedormot]

Will do. Thanks again Solarman. The plug pics were from my motor. I'm sure we will meet again here. Up until the last few days, I was beginning to think I got screwed on this motor. I also was losing confidence in my own abilities. With your help, I am feeling better about both. From the vicinity of Erie, PA., Happy boating to you and your family.

[D'oh999]

https://www.crowleymarine.com/suzuki...arburetor-dt85

Ok, DT85, 3 Cylinder. Blue Circled, show Jet Pilot, 1/4-about 1/2rd throttle, but Red Circled #6 in Diagram shows Pilot Air Screw idle-1/4 throttle. Air Screw is opposite to a Jet, further out ='s leaner, further in ='s richer.

My guess, or what I would do. Is reclean the carbs "All" and turn the Pilot Air Screw in 1/2 a turn, and the Pilot Jet out 1/4-1/2 turn

[Solarman]

D'o999, we are both looking at Adam's pics with blue & red circles.

Firstly the red circles are air-fuel mixture screws for idle. These should be set per manual specs, and in most cases they only give one adjustment in the manual, and all carbs should be set identically.

Secondly, the blue circles for the top and middle carbs are only used to adjust the amount (less or more) of (pre-mixed) air-fuel mixture going past the throttle butterfly. Only the top and middle carbs have this adjustment screw. The bottom carb doesn't have this screw.

The blue circle on the bottom carb is only the idle stop screw.

The pics of the three plugs are for a different DT85 motor that does not have the top and middle carb throttle butterfly (bypass) adjustment screws.

Adam's motor info was posted in March of '22, but Nedormot's pics are from July '23.

This is why I asked Nedormot to open his own thread with his own motor info. Mostly because it is difficult to discuss more than one owners problems/motor(s) in the same thread, it can get very confusing.

Thanks D'o999 for trying. Yes, screwing the air-fuel mixture screws "in" reduces the amount of air mixing with the fuel, causing a richer fuel mixture. Likewise, backing the air-fuel mixture screws "out" increases the amount of air mixing with the fuel that causes a leaner fuel mixture. The idle pilot jets are mounted inside each carb, and are fixed jets. They are not adjustable, unless you purchase and install larger/smaller jets.

Happy boating.