Oil mix adjust screw

[TxGent40]

Have a 1986 mercury 90hp inline 6
need to know what the very top 2 adjustment screws are for and where is the oil mix adjust screw located? A pic would be helpful

 

[racerone]

Does it have a separate oil tank that is " auto blend "- ?---If so you should throw it away as far as you can and mix gas and oil at 50:1 on it.-----I would not go and adjust anything until you are sure what you are adjusting !----How long have you owned the motor ?---What is your motor doing / not doing ?

 

[TxGent40]

Haven't had it long. It was idling way to high and a buddy "said he could fix it. Yea ok. Well got to where it wouldn't idle at all. Got it to idling ok by the rocker arm but now doesn't seem to be a LOT of smoke from the motor like the oil mix isn't the same. He turned the very top adjust screw on it (there's another one just under it) but don't believe he turned the one under the very top one

 

[TxGent40]

Yes a separate tank for the oil

 

[TxGent40]

And if I take the oil tank off and just put the oil in the gas do I leave the oil tank in there or if take it out where do I plug the old oil line at so dirt an stuff don't make it's way in.
And what is the mix ratio 50:1?

 

[jimmbo]

The correct mix is 50:1

Since there are several screws that can be adjusted, each carb has an idle mixture screw, there are some on the throttle linkage(max timing, primary pickup timing) that can adjusted/misadjusted, a pic showing which ones your friend was turning will help. BTW, idle speed is only adjusted by how far the timing is retarded. Any other adjustment will mess up it up

It was mentioned to throw the oil tank as far as you can. That was GOOD Advice

 

[TxGent40]

The screw in the left with arrow to it is the one he turned

 

[jimmbo]

That looks like the Primary Pickup adjustment screw, adjusts the sync between the ignition timing and the point of where the carbs are about to begin opening.
The actual idle speed adjustment on that engine is on the side(red arrow) and to adjust it requires the throttle cable be out of the loop. Removing the barrel nut from its anchor(below yellow arrow) will allow that. The after the idle speed is set, the barrel nut is adjust to place a slight preload on the idle stop, then reanchored

 

[TxGent40]

The anchor an loop is the plastic piece that it runs thru right here with the zip tie around it. Cut zip tie, adjust idle then move the nut to fit back down in the anchor and re-zip tie it.
Sorry for all the questions. Never worked on boat motor.

 

[jimmbo]

Mine never had a zip tie. Perhaps the latch broke or a previous owner or tech didn’t close it correctly. But you have concept of how to go bout the adjustment. Just a bit of preload against the stop. Too much and it will be hard to shift out of gear, not enough and the idle speed can be inconsistent

 

[TxGent40]

Got the piece made and on. Idle is fine but have to check the shifting.