I have a twin with tower hobbies motors on it, the first thing i had to do on that motor was to loosen the carb screw and press it down.(used a quarter to press on) then retighten...This prevents air leaks at that point...As far as the gap on the low end, mine ended up looking almost closed..I used a feller guage from auto zone for the measurement....hope this helps/

On the high end try 2 and a half turns out and adjust the low end to about a 1/16 of an inch..