Idle stop screw

[sti1471]

I have an (I think) 83 80 bluestripe thunderbolt mercury motor.

While I had the engine cover off trying to adjust the high idle, I saw a screw that says "Idle Stop Screw". It is pretty far extended (almost all the way out). What is this screw for? Is this the screw that I adjust to adjust my idle while in neutral? It currently idles at 2000 RPM in neutral.

I read somewhere that I should be able to slide a piece of paper between the idle stop screw and the stop, and it should have some friction removing the paper, but not tear the paper. Is this true?

Also there is a smaller screw above it that is pressing against an arm of some kind (I think the throttle arm) and it is almost screwed in all the way.

I am making adjustments because the boat runs idles fine in and out of the water. Goes into gear and spins the prop out of water, but IN the water it stalls when going into reverse or forward gear right away. I am thinking that the adjustments are off and it is flooding.

Is there a screw that adjust the idle / fuel mix when the boat is in gear, and a different screw for neutral idle adjustment, or are they both the same screw.

Thanks all.

[MacDaddy21]

The idle stop screw controls the rpms of your engine while in idle. 2000 rpms is too high. My 1979 402 40 hp is supposed to idle at
approximately 650 rpms. I do not know what it is supposed to be for yours but it can be found in your manual.

The screw to adjust idle mixture is on the carburetor(s). It is a flat head screw on the face of the carburetor. I looked at the schematic for your motor and it is sort of hard to tell exactly where it is located, but it should be a silver colored flat head screw, and if you
completely remove it, it should have a spring on the inside and have a long pointed needle-like end past the threads. There is a
process to link and sync your carbs which will get the mixtures the same, which can also be found in your manual, if you have one.