Exhuast mods

do not just remove the whole end cap, what can be done is to pull it, look at the inner most tip of the tube, there is a cone shaped piece on it that is supposdly the spark arrestor, that can be cut off for more direct flow, but nothing you can do to a stock silencer is going to give you much if any gains.
even adding just an aftermarket silencer may only give a very slight gain, the only real gain is with a full aftermarket expansion chamber/silencer and rejetting
 
i have no personal experience with any 30mm's
and nobody can tell you exactly what your jetting should be.
what i can tell you is...

1.set the floats
http://www.blasterforum.com/carburetor-138/float-heights-how-adjust-them-50565/

2. adjust airscrew/pilot
http://www.blasterforum.com/carburetor-138/adjusting-your-airscrew-pilot-jet-51060/

3. lower the needle clip until it rich bogs, then back up till it pulls hard

4. plug chop to determine the main jet
http://www.blasterforum.com/do-yourself-20/how-plug-chop-38674/

here's some other 30mm threads, (the 30mm oko is the same as the keihin)
read thru them and see if you can find a "starting point" for jetting............

http://www.blasterforum.com/searchresults.php?cx=partner-pub-9438014176008015%3A9127094460&cof=FORID%3A9&q=30mm+jetting&sa=Go