The cold idle solenoids used by Kawasaki to boost engine idle speed until the engine is warm enough to run on its own (shown circled above) have been the subject of hundreds of not thousands of forum posts. Most riders don't even know they're there until they modify the intake. Then it's decision time. Do you keep them and put up with the racket or do you remove them and manually bump the cold idle (using the fast idle knob, throttle lock or other means) for a minute or so while the engine warms? Bruce Anderson dug into the problem and found a cure. There's a downside. It really only works for those who've done the Caddman intake modification and have left the left side air cleaner cover in place. Read his description to learn why.
I did the single side Caddman with K&N parts and heard the racket from the relays when the engine is started cold. I ride in cold weather often and didn’t really want to lose the relays, so I took a harder look at the problem. The noise we hear isn’t really the relays “clicking”, it is the sound of the air rushing in through the tubes, like a huge vacuum leak which goes up and down with engine RPM.
To get rid of most of the noise all you have to do is grab two 19 inch pieces of 5/16th inch fuel line. On each relay there is an unconnected tubing port (see picture, red circles). Just plug one piece of fuel line onto each of the air relays and feed the fuel lines into the air tube (blue circle). 19” seems to allow it to get all the way to the other side. If you don’t go all the way, the noise actually seems to get a little worse because it echo’s down the air tube.
This fix causes the noise to move over to the other side, which makes it almost silent if you still have the stock air cleaner. If you have done Caddman on both sides, this will probably not have much of an effect, it will just move the sound to the other side.