What did you mean the air cleaner hits the float? 
That should have been air cleaner
stud ( I deleated the post after I realized it would lead to flooding of the carb, like I experianced years ago when a friend installed the air cleaner stud in the slot in front of the air cleaner stud hole....yes a 1/4-20 stud will fit and push the float down).
The power piston usually isn't an issue unless you have really wild cam and aren't producing a ton of vacuum which you can also compensate for with a lighter spring.
JET and SMI use the screw to to adjust the part throttle mixture.