Occasional knock in engine?

When idling, my 1982 KZ750H3's engine will sometimes knock or tap deep inside. If you have a finger on the valve cover or elsewhere on the engine you can feel it when it happens...as if something inside the engine is banging against something else. It is not a timing chain noise. This only happens once in...say, every minute or two, and it never happens at any rpm above idle. At first I thought it might be a miss, but it seems stronger then that. Engine runs fine otherwise. Engine upper end was rebuilt 5 months ago. Wires and plugs are new. Coils are old.

Any ideas where to look first? Thanks!

Searching on the Ma Kaw website I couldn't find and H3 for 82. All the 750 engines I saw showed a HiVo chain between the crankshaft and the transmission. The chains have be known to cause a knock like that on an engine the idles a little bit rough. the earlier bikes had a single row chain much like the drive chain that was even noisier. If that is the problem it is the transmission gears knocking as the chain loosens with slack and tightening again when engine gets past the skip. Most of our engines with the chain instead a gear connection make the noise. Can't do much about it since the chains are almost if not totally impossible to find so we live with it.
It's just a quirk of these old Kaws. :silly: :silly: :silly:

Yea, the '82 H3 is on the Kawa website, but you have to search hard to find it (I think it's under the LTD's).

Actually, I had come to expect that the primary chain might be the cause. Which is why I always hear that it's good to keep the carbs synced. I have heard that the primary chain (isn't that what it's called?) between the crank and trans is pretty much bullet proof, even if it streches a tiny bit, but it is irritating. Guess I'll resync the carbs and see if that helps. But it does seem to have an occasional miss, and I've been wondering if it might be the old coils.

My 750 twin was doing similar and it was the timing advancer which was messed up putting the timing too far advanced at idle.