Rejetting is only required if you let that sucker breathe by modifing the stock air box or replaced with a aftermarket air box.
I followed Russ Wolf recommendations for performance mods in 2007 and glad I did. My 800 Runs Tuff.
rejetting your Vulcan 800 you will need:
165 main jet
50 slow jet
Fuel Needle (aftermarket adjustable)
The stock needle is not adjustable and can,t be used.
I got my needle DNO 106 from DynoJet kit 2147 but the jets were not the right size and cost almost $80. High price for just a needle. There is a better deal
The needle,165 main jet, shim washers, E-Clip,can be bought from the Kuryakyn.com it is Jet Kit #8562 for Vulcan 800
All for $36.99. This kit has everything needed for rejetting EXCEPT
the 50 slow jet and the needle holder which can be bought at a Harley dealership. I paid less than $15 for the two. you can get the 50 jet and others here
Jets R Us KAWASAKI VN800 VULCAN
Getting rid of the EPA stuff, rejetting, changing intake and exhaust is well worth the time and money,
here is the set up russian Wolf recommends: Both the Dynajet and the Factory Pro needles for the 800 are the same length as the OEM needle; the real difference lies in the different taper of the aftermarket needles. The aftermarket needles flow fuel much more smoothly than the OEM needle and are, of course, adjustable. What you want is to put the e-clip in the third groove from the top of the needle. The shims (washers) are for more precise height adjustment; their thickness is just under half the distance between the grooves. One under/one over is the standard starting point that's been proven out over time; however, as always, each engine/carb combination is unique, so obviously fine-tuning is necessary. BTW, the one over the e-clip is to put just a slight weight on the needle to prevent possible "needle float" during high-speed runs or abrupt throttle chops.