Simple

[merc850]

There's a simple way to check for fuel in the carbs and fuel flow; tilt the motor all the way up then pump the fuel bulb, if fuel runs out of the carb throat(s) then it's probable that all's clear. This can also be used to flush the system.
To clean the carb(s) remove the low speed needle(s) and the hi speed jet screw plug(s) then spray PowerTune from Mercury into the openings, the PT should spray into the carb throat(s) cleaning the passages out.

 

[jimmbo]

I've used that Power Tune Method, and sometimes it does work. Other Times it has dislodged a clump of Varnish/Gum, and plugged up one of the Fuel Circuits. Disassembly of the Carbs, including all the Mini-core plugs and then you can get any guck out, is really the only Proper Way to clean the Carb(s)

 

[Chris1956]

On Merc sidebowl carbs, the idle restrictor tube can be cleaned by pulling the brass plug on the upper port side of the carb body. If the main jet plug is also removed, the gum out can possibly flush it out, along with the main jet. the idle mixture screw allows you access to clean the air passages only.

This is the "gorilla" way to clean a carb, and may not work in all cases. If you clog a carb, the cylinders it feeds are starved of fuel and oil. No good for two cycle motors. They will overheat and scratch up the cylinder walls.

 

[merc850]

The idea is to de-gum the passages, like using injector cleaner in an auto.
Sorry I posted it.