knocking noise from motor

i have a kz400 that the factory mufflers were shot so i took them off and had sportster mufflers mouned on the bike the mufflers had baffles drilled out a bit.heres my problem since installing the sportys i have a knockin noise coming from the motor during idle only,any kind oif throttle and it disappears,it never did this before,could it be the exhaust?

Yes, but more like an exhaust leak. Did you install new exhaust gaskets, or reuse the old ones?

there were no gaskets it was 2 u shaped pieces and the the outside round piece with the bolt holes.

Well, there's your problem. Gotta have um. Get a set of exhaust gaskets from Z1... or if you're in the EU area, I believe there's a good provider there... install them and I'll bet the knocking goes away.

!Seymore is absolutely right; without the gaskets you will have exhaust leaks and they can make quite a bit of noise. Notice in the diagram below the items marked #5. It's possible yours were there but you didn't see them because they were stuck up in the cylinder head and hard to notice. If so, be sure to remove them when you install the new ones; you don't want to double them up. If the old ones are there they most likely should be replaced in any event, so I would toss the old ones. Ed

Good points Ed. I had not even thought they could be hardened in the opening and not coming out on their own.

Shawn, please do get good light on the situation and see if there are hardened gaskets in there. Remove and replace, if this is the case.

Keep us posted...

the old gaskets were in there i got them out and ordered new ones already,hopefully this takes care of it

10-4. Keep us posted...

well finally had time to replace gaskets and put pipes back on,knocking noise is still there,sounds like its on the rightside underneath the side cover with kawasaki stamped in it,again once any throttle is given it disappears until it comes back to idle

Is it a tap? or a knock?

I have a tap - which i am thinking is either valve clearances or an exhaust leak.

Question to all-- when there is an exhaust leak - do you always feel the puff from the pipe area? or is it possible to not feel a puff, and still have a leak?

more of a knock

Mine does the exact same thing, I have two into one exhaust, it's a knocking from the clutch areah, but disappears right when I hit the throttle, is it possible it's the primary chain? Curious if anyone has a solution to this.