Bro reason for closing secondary air intake system...means air pipe from solenoid to valve cover...my bike have this same rattling sound in specified rpm range....engine rattle possible fix
I have been riding since the mid 60's and just recently bought a cbr250r. It has rattled since day one at 5,500 to 7,000 rpm but it ran very strong.
I waited until after my 600 mile service (which went well and everything was fine other than 2 valve shims had to be replaced). The rattle was still there.
I was curious about the pair valve which is located on the valve cover. I removed the reed valve and the port plate below the reed valve. The port plate was totally loose in there. It is a very inexpensive part, stamped steel plate with holes to direct air to the pair valve. I removed the plate, put everything back together and disabled the pair valve by plugging the air line going in and capping the fitting going out. THE RATTLE IS GONE!
It instantly went from sounding like the engine was going to self destruct to a sweet sounding machine.