loosing top end RPMs

[Waltg1296]

1991 Yamaha 175 only turning 4700 RPM's at top end. I had the carbs cleaned last season and it ran pretty good. But I have I began expierencing the engine shutting down at low idle and sneezing. I have sprayed carb cleaner in all three and have tried adjusting the carbs and can make some minor changes to the top speed.
What process should I use in adjusting the carbs. Are there factory settings? I am adjusting the adjusting screws on each side of the 3 carbs. There are 6 screws total. Should the carbs all be set the same? I am doing the adjustments in the water at different speeds.

 

[rodbolt]

Re: loosing top end RPMs

first pull the carbs and carefully clean the idle and main circuits. pay close attention to the idle fuel jet and the main jet and associated passages, then replace the fuel pumps and flush the lines.
the adjusting screws just vary the amount of the air/fuel metered by the pilot jetting.
keep messing about and you will find what lean running does to pistons.
the initial setting on the pilot screws should be about 1 3/8ths turns out from lightly seated. from there if everything is correct will be less than 1/4 turn in or out.
I dont care if the carbs were done this morning, if they get dirty by lunchtime they have to be done before dinner.
spraying carb cleaner down the throats just washes the lubrication from the shiney parts and wastes carb cleaner.