Fix for 81 KZ650H Air Ducts

Sharing this design from my fab shop for any 1981 KZ650H owners that can't find any NOS air ducts, but don't want to fight with pods or re-softening their air ducts. The design utilizes cutting the front off of a pre1980 airbox and riveting it to the front of the 1981 air box. You can then purchase brand new pre-1980 air ducts to use as needed. All work and credit goes to Urban East in Virginia.

Did they glue the new front to the airbox? .... or seal it to make it air tight?

By any chance did you consider swapping airboxes? I'm not sure if this will work, though.




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The 79 airbox front was cut off, and then glued and riveted to the front of the 1981 airbox. The seam around the piece glued on was then sealed with painted-on silicone sealant. I had the 79 airbox to actually see if it would fit on the 81 frame, which come to find out it will not.

We're supposed to have some dry weather Sunday, so I'll go out and install it then. The 79 air ducts fit perfectly into this air box however, and the mechanic/fab shop knows their way around vintage motorcycles so I trust this design will work out alright.

Thanks. I'm kinda surprised they didn't go with individual pod filters or did you nix that idea?

A couple of alternatives for the 81 CSR for future reference in case someone stumbles across this topic.
One option is to cut donuts from radiator hose & use the later csr ducts >> they're the same as the 750-4 ducts.
I think you'd need two difference sized rad hoses & use 2 donuts per carb. then use good ss band clamps. this has been done.
Or install BS32s from an 82-83 CSR along w the later ducts >> a pricy option, but I think there would be a performance increase with cv carbs

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I attempted pod filters using some mid-tier priced ones, and had nothing but issues and couldn't get the bike to run right even with what should have been a good ballpark jet range. The carbs do need a sync, but I just couldn't dial in the pods, so that idea has been sent to the trash.

I looked into all of your ideas Martin, and had good luck with the radiator hose idea a while back. It was a pain to put each duct in place though using the design I fabbed, so this airbox idea may be the best "bang for your buck" if you don't want to have to change anything besides air ducts. I think also that anyone that has an 81 that just wants the bike to be "stock" as possible could benefit from this idea. The only thing "not stock" is the size of the holes on the airbox. Everything else matches up to 81 spec, so it's my hope this idea helps someone along the way. Considering it only cost me $100 in parts and labor, it's quite feasible for most owners.

Thanks. By any chance do you know what adhesive they used? I'd guess ABS glue. or maybe Seal-All but I'm not sure how well known seal-all is.




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