Depends on what class you are attempting to run.
We run 10 of these 540's in GP-ModXR class with much success in bone stock condition as delivered from the factory.
The Carb is the weak point, very lean low speed jets.
No Billet Parts available commercially unless you machine them yourself.
The Mikuni Flat Slide will be Illegal in most classes.
The cam is actualy quite large in stock format.
The stock Valve springs are decent, they usually do not float until around 5.5k rpm.
DO NOT run this engine without a governor with the stock flywheel, the counter weight will come apart
very quickly.
We found much success with this Kawsaki FC540V engine, especially of you just leave it alone and run it stock.