The flapper valve is an intake noise control device.what is the flapper mod.i own a rc51 2004 and heard of some tool on ebay to remove that.
thanks for info subsailor.The flapper valve is an intake noise control device.
It blocks off halve of the air intake between 5-7K RPM.
It also causes a dip in the power band between that RPM range.
By disabling the flapper valve, you not only get a better power spread, but reduce the bike's weight when all that junk is removed.