1983 KZ250 Single Engine Tapping

Hi all,
My 1983 KZ250 single it tapping in the top end of the motor. Recently I took the top end apart to replace all the cylinder gaskets. Before removing the cam sprocket I lined up the timing marks on my rotor and TDC. The motor is now back together, replaced the oil and put in a new spark plug. The valve clearances are in spec with my workshop manual and there is proper tension on the cam chain. I have also checked the exhaust manifold. The bike starts, idles and revs but the tapping stays in rhythm with the rpm. This bike has an IC ignitor unit. Any suggestions?

It's worth mentioning that the bike was working and not tapping before the rebuild. This bike has the IC ignitor unit.

I cleaned up all the electronics on the bike before putting it back together. Checked all the wires and grounds.

My original issue was not getting a proper spark. Every time I turned on the kill switch the spark plug would fire once on its own and then nothing while the bike turned over.

Looking closer at the pickup coil, I noticed a small 2 pin belt harness part number 26001-1729. Once I removed it, the bike sparked and I got it running with that tapping noise. I reckon that little belt harness assists the timing advance but I can't find any info online about it.

Any information would be great. I would like to know if I need to replace this belt harness or the IC ignitor unit.

Bbil wrote: It's worth mentioning that the bike was working and not tapping before the rebuild.

Did you ever check your valve clearances before the rebuild for comparison?

I found the same thing with my KZ250. I checked the valves and found the gap was too small, so I set them to within spec. Then they were noisy. I think they are just noisy when they are in spec. Setting them to the lower value of the service limits should help. Since they're so easy to adjust there's no harm in setting them to the lower value as you can check and adjust more frequently if need be.

Another thing to check for is exhaust leaks, if the copper o-ring at the exhaust is leaking slightly you may get a little 'pop' with each power stroke, and it can sound a lot like a engine tapping.

Thanks mate,

I tired adjusting my valve clearances to spec and then tightened them right up. Still sounded the same and made no difference.

I put a new exhaust gasket in, applied muffler putty to the manifold and an extra muffler sealant to the seams to ensure no leaks. It made no difference.

Do you know anything about that 2 pin short belt harness that sits between the pickup coil and main wire harness? I have attached a picture.