Knock....knock....knock....knock

My KZ650 is making a not-always-perfectly rhytmic knock under acceleration, even very light acceleration. Hard acceleration doesn't seem to make it worse and may even reduce the knocking. I've heard it in all 5 gears, but it's most pronounced on the lower 2 gears - perhaps because there's no wind noise to muffle things.

The sound isn't constant in that it doesn't always appear and the intensity varies from time to time. There is no knock under deceleration.

At first I expected a stiff link in the chain because the knocks are too far separated to come from either sprocket. But there are no stiff links. Sprockets appear to be in decent condition, as is the chain.

Anybody experiences anything similar? Or have any idea what it could be other than the chain?

make shure the exhaust isn't hitting

Checked the primary and cam chains for tightness?

motor knocking from bad fuel or timing ????

Thank you both for the hints, but nothing hits the exhaust.

Why would a tight or slack cam- or primary chain give knocks with such long intervals and for what reason? If they can make this kind of sound I'd like to learn about it.

It doesn't sound like chain slop, it sounds more like a bad bearing or the chain being caught on a tooth or being forced to bend when it doesn't want to. Only all wheel bearings turn freely and smoothly and there is no slop on the wheel or swingarm.

Street Fighter LTD wrote: motor knocking from bad fuel or timing ????

No, it's not anything like pinging and that would be more rapid. It comes from the chain area - which could mean anything between output sprocket and rear wheel.

roll the bike fast, like down a small hill and listen with the motor turned off. see if you can eliminate motor or drive chain

I can try that sans helmet, but as mentioned there are no sound under trailing throttle.

Well, after bending each link, cleaning and lubing the chain, the noise is gone Not sure if it's the bending or the cleaning or the lube that did the trick, but things are quiet now.