By adding the new reed cage you have added air. I would think that by turning the screw you just changed your idle mixture. Not being familiar with that carb I'm not for sure...but I would think to richen the mixture you would need to step up to a large jet. I think by doing so you'll pick up some. I really do not think the screw changed the mixture of the mains.
Look at your manual or pull the carb and look at the numbers on the jets. You can probably play with a few jets until you get it just right. I would say when you are running you are probably running a bit lean. Do you premix?? If so that can be bad. I know the crossflow johnnyrudes can run without the breather attached and sound pretty sweet...maybe pick up just a hair on holeshot...but not noticable...the loopers though can burn up if you are running them tight without the breather. They lean out. After putting the reed cage in it you have added more air but without a jet change I don't think you have gotten all your potential and may be in a dangerous area without more fuel. I may be wrong on it...but I would check and see. Anytime you add more air...you need to add more fuel to get full potential...if you premix and have too much air...that spells for disaster. All I'm saying is make sure you have enough fuel for your additional air and flow.
Check it out and let us know...then you can to play with the exhaust some...:D...maybe a hole in the midsection!! Would sound like a chainsaw on roids!!
"But if serving the Lord seems undesirable to you, then choose for yourselves this day whom you will serve, whether the gods your ancestors served beyond the Euphrates, or the gods of the Amorites, in whose land you are living. But as for me and my household, we will serve the Lord.” Joshua 25:15