2007 yamaha 25MSH back fires

[mvharwood]

This outboard of my grandson seems to have a problem with the needle valve.We have tried carb cleaning but i believe the needle valve is below a "cap" and is not getting clean. Can that cap be removed and then valve removed and all cleaned properly. If so what precautions should i take when doing this.?
Also this is a 2 stroke is it recommend that unit be ultrasonically cleaned or is just using a good carb cleaner and soaking it for a couple of hours ok. ?

[boats.net]

Those are tamper proof plugs required by the EPA to prevent carb settings from being adjusted. The plug can be drilled out(use a drill stop set at about 3mm so drill bit doesn't damage screw or carb) for cleaning carbs, count the number of turn needles are set at and after cleaning set needles back to same setting and replace plug.