175 hp carbureted 1990 model sync & timing

[Kongfish]

I have a 1990 Mercury 175 carbureted 2 stroke RX4
I had it running perfect and the cam roller cracked and fell off, after replacing it and using the manual to set it back to its right position. I started tinkering and got the motor off a little , then a little more, and then finally it would not even crank. I fixed that, sorta. I used a old photo I took awhile back to zoom into the three screws I tinkered with and I set the screws back to as close to where they went per the photo and it fired right up and sounded right. When I ran the motor it took off and runs good at wot. But if I back it down to under 3/4 throttle it wants to just die off. If I have it at half throttle it fells like something is being held back which is the best way to improve my problem

[Ski]

Your on that "slippery slope". The approach you need to take is to start from the beginning with the rigging. When the carbs are out of sync ones trying to spool up the motor and the others are loading it with fuel. Start with a fresh set of plugs and start on page one.

[Kongfish]

Ok,
So now I have referred back to a old photo and set the screws back to as close to the photo as possible. That worked 100% better than I would have ever guessed, it fired right up on the 1st. Try, it idiled fine, maybe a just tab high but I can now work in 1/4 & 1/2 turns trying to get it adjusted correctly.
Now the only problem I have to correct is one last throttling issue.
When I take off from an idel to "WOT" it starts off fine gets up on plane but then it feels like something is just a coots hair off, it feels like something is holding it back from wanting to just let go & free it completely up.
It's like something has a set of rains on it and its trying to just last off but whatever it is that's off, it just won't set it free to go and go.
What position should the carburetor butterflies be at with the throttle being WOP? Guessing at my problem I think it might be that it needs more air and I have not got the butterflies set like they should be at in the ( WOT ) .

[Kongfish]

Does anyone know what these three screws do ?
On my motor I have screw
#1 it's located up top and it is a called the timing advance screw.
#2 it's the bottom screw that is called the idil stop screw.
#3 it's the throttle position ---- ?? It's the next screw down from the timing advance screw but on the same arm as the advance timing screw?
Which should I attempt to alter to get more air, or more fuel or more or less advance timing?