Mystery noise.

I have a mysterious noise coming from my bike. It sounds like it's coming from the front cylinder, cylinderhead or throttle body. The noise is a light (not loud) knock. It happens when I blip the throttle and let it close quickly. The 'knock' occurs as the revs drop. It doesn't seem to happen when I slowly close the throttle as the revs drop more slowly. I've only really noticed this noise since doing the valve clearances and so I'm wondering if I've f**ked up somewhere. The bike is running perfectly otherwise with no untoward rattles.

Has anyone got any suggestions before I start investingating further?

[Sid Squid]

It's not possible to gauge precisely how it sounds from our description, so, attempting a different tack based upon the other info you supply, this: You've recently removed the cams in order to reset the valve clearances, yes? If so then you will, of course, have removed the cam-chain tensioners, these having been disturbed one or both may be the source of a top end noise.
I'd check there first.

I'd be suprised if it's cam chain related as the noise is a light knock/loud click and not a rattle. The bike is a K4, so it's got the ratchet type tensioners and they were free and not sticking when I put them back on. It doesn't seem to happen when the bike is cold, but it starts as the bike gets warm. It also only happens after 'blipping' the throttle to say 4k. Then as the revs drop the noise happens at about 1k. I thought at first it might be a throttle butterfly sticking open and then snapping shut under the vacuum from the engine, but having had the top off the airbox all the butterflys seem to be working fine.

how is the oil level?

[Sid Squid]

Originally Posted by madness

I'd be suprised if it's cam chain related as the noise is a light knock/loud click and not a rattle.

Quite, it doesn't seem the right noise, (but as mentioned noises are very difficult to communicate in written form), however when anything doesn't work/look/sound right after it's been distubed even in the most minor way, my first resort is to check all that's been affected.

Thanks everyone for you suggestions. Having investigated, I have found the source of the noise.

The noise is being made by the PAIR solenoid. It makes a noise at all temperatures, but gets louder as the engine gets hotter. I never had this noise before, so I assume that the solenoid wasn't previously working or that disturbing it when removing the air box has made in noisier. At least I now know that it's nothing detrimental, so I can live with it.

what does the pair solenoid control, my k3 has made a sound very similar to what you describe since i bought it 2 years ago....

The PAIR solenoid controls a pulse of air that is sent to each exhaust/cylinderhead to help with emissions. I don't think it makes any difference to anything else, such as performance. Some Minitwin racers remove it all together.

[yorkie_chris]

Just excess weight.

I have the exact same noise on my SV K3, glad it's not something to worry about!