strange noise

Hello guys! So over the winter I picked up another bike. This one being a 1981 Kz750 ltd. Starts and runs, drives fine. It has developed a strange noise first noticeable around 1200rpm. Gets louder/more pronounced the lower the rpms. Idling around a grand sounds like its gonna break. I don't even know how to explain the noise.. But it isn't noticeable when I ride or idle at 15 grand... It seems to appear on the right side of the motor. Maybe lower end or middle? Can't hear it much on the left side.. I'll try to take video of it. Any ideas? The bike has about 36,000 miles on it. Maybe cam chain? Or tensioner? Possible valve Noise? I don't even know what to look up to see if it's somewhere in another post.

The FIRST thing you should do is check the valve clearances. Then the cam chain adjuster if you have a manual one. The noise could be the carbs being out of sync. These engines can make frightening noises at idle like that. You also need a MANUAL.
Steve

A disturbing sound at low idle rpm -- like digesting nails -- can usually be reduced or eliminated by a good carb sync.

And a good carb sync is predicated by valve clearances within spec, healthy fat blue properly timed spark, correct fuel levels, and ample fresh clean fuel supply.

Good Fortune!

For a free downloadable KZ750 4-cyl service manual, use this link, and scroll down to "The Bible" ---

mbsween.bike-night.com/kz750l3/index.html

Good Fortune!

Thanks for the fast replies! I'll start looking for a valve cover gasket and the end caps, also a vacuum gauge to sync the carbs. There's a link that shows the noise is making at 1000rpm

Classic stumbling caused by out of sync carbs.
Steve

Sounds like piston and cam chain slap from unbalanced cylinder fire, usually associated with misadjusted and unbalanced carbs.

The smaller fours seem to make more noise than the large ones, still mine can make some alarming noises when out of sync.
Steve

Still making noise at a grand idle. Carbs ae synced. I think it may be the chain tensioner? I believe it's an automatic tensioner, it Has a lock screw in it. Any ideas guys?

Are valve clearances within specs?

If mechanical timing advancer is fitted, would assure correct ignition timing at idle rpm and that the advancer is in good serviceable condition. clean and lubed.

Good Fortune!

Yes, valve clearances are in spec. Visually looking at the advancer it looks fine.

Would check for alignment of advancer F mark with timing light at idle rpm.

Good Fortune!