What is a normal amount of turns from the default for mixture screw

[rdhj]

I am trying to get the mixture correct for my DT 9.9 from 1987. I have started at 1 and 1/2 turns out from lightly seated. The motor sputters a little bit and I'm wondering whether it still needs to be richened up some more. What would be a normal amount of turns from the default one and a half that you would expect? At what point would you have gone too far signifying that something else is wrong?

 

[GA_Boater]

There is no default setting. You start with 1 to 1 1/2 turns out and fine tune with the motor in the water and idling in gear. Turn the screw in until it starts to sputter, then back it out until it sputters again. Set the screw in the middle by counting turns or partial turns.

The motor must be in the water and in gear because of exhaust back pressure and load.

 

[Scott Danforth]

Being a 31 year old motor, is this new to you? Was it running prior?

You may need to pull the carb and pull it apart to clean it

 

[rdhj]

I have cleaned this carb out tons already and the pilot circuit appears to be flowing fine from the hole near the choke plate to the mixture screw...any idea how i should clean from where the gas comes from the bowl to the top of the carb....i assume it gets the fuel from the main jet nozzle? I have cleaned every hole on this carb a bunch of times...

alos, just tried messing with the mixture screw and it doesn't sound as the RPMs are changing as i turn it in or out.....have a digital tach on the way that I will hook up and see where I am at.

Ran the motor last night when i was duck hunting and it seemed OK with the exception of it randomly stuttering as I was accelarting and i got some cavitation which
\\ many be due to my busted up prop...weird thing is it never cavitated the last 4 times i had the motor out.

 

[jimmbo]

When you put the carb back together, did you check the float setting and adjust if necessary? The initial setting of 1 1/2 turns is almost always too rich, but it will allow the engine to run. An indication of something else being wrong is when adjusting the mixture screw has little or no effect. Does the engine die if the screw is turned in all the way? Is the throttle plate fully closed at idle?

 

[rdhj]

When you put the carb back together, did you check the float setting and adjust if necessary? The initial setting of 1 1/2 turns is almost always too rich, but it will allow the engine to run. An indication of something else being wrong is when adjusting the mixture screw has little or no effect. Does the engine die if the screw is turned in all the way? Is the throttle plate fully closed at idle?

yes, i check the float height the other day and made a small adjustment as it seemed a little off..yes, when i turn the screw all the way in, it will stall...not sure if the throttle plate is fully closed at idle...guessing it should be? i noticed the two pilot holes and how the one hole is behind the plate when fully closed...what is the function of this hole? what happens if the plate is not fully closed at idle?

 

[jimmbo]

Pilot holes?
There are fuel ports in the carb throat behind and in front of the throttle plate. That is where the fuel discharges at idle speeds and at speeds until the throttle opens enough for there to be enough airflow for pull fuel through the main nozzle. On these engines, the carbs are supposed to be completely closed at idle speed and idle speed is controlled by spark timing. The carbs remain closed until the timing is advanced to what is referred to as the primary pickup. The carbs will open slowly until max spark advance is attained, then any further movement of throttle lever opens the carbs fully. That is one of the reasons the link and sync is important
Some carbs have holes in the throttle plate, to get enough air so the engine can run with the plate fully closed. Are those what you car calling pilot holes

 

[rdhj]

yes, didn't know they were called fuel ports....the only issue I seem to have now is the couple times it hesitates or burps as I am accelerating. as far as I can tell the carb is clean and flowing....any ideas what it could be?

 

[jimmbo]

Well if those little ports are plugged up even a little, then the is too lean at off idle, same goes if the float is set too low, or too high for that matter. If the carb is out of sync with the spark advance, the engine may hesitate. I am assuming this engine is a 2 stroke

 

[rdhj]

Well if those little ports are plugged up even a little, then the is too lean at off idle, same goes if the float is set too low, or too high for that matter. If the carb is out of sync with the spark advance, the engine may hesitate. I am assuming this engine is a 2 stroke

should the float be set dead level when the pin is just touching the tab? what does it mean by synching the carb to the spark advance. how would this be checked? and yes, this is a 2 stroke engine.

 

[jimmbo]

Do you have a service manual? One from the engine manufacturer, if not get one
On most carbs, but not all, so that's why the manual is important, the float is often set by inverting the carb body and having what is now the bottom of the float parallel to the carb body.
The syncing of the carb to the spark advance, is the engine being at the correct speeds as the carb is opened. Most modern 2 strokes would advance the timing fully before the majority of carb opening occurred. I did say majority of opening, however there was a small amount of opening occurring as the timing reached a predetermined point, that did allow the engine to breathe. It also allowed once the engine was at higher rpms to close the throttles significantly while still maintaining full spark advance. The rpms only dropped a little but it helped fuel economy significantly. This adjustment also be explained in the manual. It should be checked/adjusted anytime the carb has been reinstalled after being removed from the engine, a slight change in position or a different gasket could change the calibration

 

[rdhj]

I ordered a service manual last night from ebay so I will check out some of the things you suggested. I was wondering. If the throttle plate is supposed to be closed at idle, what is the purpose of the idle adjustment screw? This screw if turned in will open the throttle plate a little to allow the motor to idle correctly and then will no longer be closed at idle. Is the correct idle speed supposed to occur when the plate is closed.

 

[99yam40]

most T Plates are held open a small amount by the idle speed screw, very few have holes drilled thru the plates
I have no idea about that old Suzuki