Yes, I'm pretty sure no matter which reed valve system you choose, you will have to lower your main jet, one size. With the V-Force reed valve, you have to cut off the "wings" that are attached to the rubber air boot between the carb and the reed block. Once you do this, you can't reverse back to the stock system, unless you buy the new rubber piece. I'm not sure if you have to do this on the Boyesen or not, but I would assume so. Then again, I don't know why'd you want to go back to stock either.