what determines the fuel height in the bowl is those pins, or the fork shaped thing in the carb.
the float pushes them UP, and closes the valve attached to the fuel intake.
so with the pins bent down, the float will lift them up earlier, closing the valve earlier, therefore the fuel in the bowl will be lower.
now, with the fuel lower in the bowl, the distance the vacuum in the throat of the carby has to pull fuel up from the bowl is greater. gravity sucks, remember! fuel has weight! this is basically equivalent to either less vacuum,(which wont change for a given speed anyway so forget about that) or a smaller jet... but note! only a very very very tiny little bit smaller!
the reverse applies if you bend them UP towards the carb...which can lead to incessant flooding if you overdo it!
i prefer having the fuel lower. i can live with a slight "miss" when i hit a big bump (the fuel sloshes around and the jet gets exposed briefly) rather than having to turn the fuel tap off all the time and getting crankcases full of fuel
usually tune with 0.05mm increments, thats what sizes metric micro-drills come in. (theres others but they cost as much singly as a full set of 20 standard ones do...about $20-$30) fractional/number drills are imperial and have slightly different sizes...handy for the ultra fine tune but not really required unless you really get into it. you also need one really good drilling machine to get them accurate enough to warrant the expense! all drills drill slightly oversize. process is simple. fill hole with solder, remove excess solder from inside of jet with drill until it reaches the brass of the jet again, then drill the tiny little jet hole itself.
the super fine copper wire works just as well... try things like the wires in headphones...just one strand of it at a time! if you can solder it at least without blocking the jet!
:wacko
h yeah... and it gets a lot hotter if you have to get off in a hurry!