The “Moog Mod” air-duct replacement tip

This article is an edited version of a KTOF post by member “AtLarge”, about his 1983 KZ750-K1 LTD  (reprinted/edited with his permission).  The original can be found here:  “I call this the Moog mod.

…And this important caveat from the author, “…the earlier bikes have 38mm carbs where as mine is 34mm so keep that in mind. If your using it on other models there are probably other bellows at the auto parts store that would work if this one won’t fit for you. Just go during a slow time and have the counter guys help you rummage through the shelves. Most of them are pretty good sports.”

I needed replacement intake air ducts, because I had one good intake duct and one off of something else.  As I’m sure the rest of you 750 people know, the ducts are very hard to come by.  Frankly, I wasn’t all that pleased with the design anyway, so I stopped hunting for one and came up with my own.

Moog mod, side view, on bike

Moog mod, side view, on bike

Here’s what I used:  Rack and pinion bellows for a Prizm.  You can buy them right online from O’Reilly….

Item No: K9321

$26.99 per Box (at this writing)

Moog R/P Bellows

Moog R/P Bellows

Bought two new ones and cut them to fit.  Works great.  Has some give, so it will handle the vibration.  Much easier to connect to the carbs, and seals better than the originals I think, too.  I haven’t put the carb clamps on yet because I don’t have any.  I’m working on that next but it’s such a nice snug fit I almost don’t think it’s necessary.  It’s automotive grade rubber so it should be okay with the heat.

Did all the work on it while the air box was still in the frame too which was no small feat I might add.  Still retained all the original components (except the ducts).

Here’s a shot of the business end.

Moog mod, inside airbox view

Moog mod, inside airbox view

Here’s a shot showing the bellows are actually sandwiched in between the clamps.  The seal is impervious to water.  All the air must pass through the air box opening and the filter.

Moog mod, bellows-clamp view

Moog mod, bellows-clamp view

Note from Biquetoast:  Please note that I have not done this/these mod(s) myself, so I cannot validate any of the claims here, nor do I know the models for which this will work.  Although if you’re a 750 twin rider like me and AtLarge, you will likely face the need to find replacements like this someday too.  So if you ever try this, please let me know and I will update this page if I ever do this as well.  Good luck!!


  1. Steve Wood

    I have the same airbox on my 83 KZ-K1 and can not find an air filter replacement that fits and the bike shop is reseaching it also., there all about 3/4″ too tall. mine is 6 1/4″ tall not including the foam ends. Please help!

  2. laurie brown

    I used the filter for a KZ750 from K&N and cut it down by 3/4 inch then formed a new gasket end from black Permatex silicone
    It looked original

  3. AtLarge

    Air filters for the late model KZ750 twin 11013-1045 can be substituted with the same filter from the Kawasaki ER500 1999-2006 11013-1261. HiFlo makes an HFA2502 that fits perfectly just by trimming the lower foam gasket OD with scissors. This excellent tip was provided by Michael from another great source of KZ & Z twin knowledge.

  4. Biquetoast

    @ AtLarge –
    Hey man, good to hear from you.. and thanks for the tip!

  5. Jonathon England

    THis is a long ago post but still really useful. I just had to try and do a single filter on each carb and then do an upgrade on the jets for the carb. DOESNT work even after 2 shops tried to make it work. I ended up putting silicon on the ducts because I couldnt find a solution. YOURS IS AWESOME. THank you so much for this.

  6. Biquetoast (Post author)

    @ Jonathan –

    Right on. And thanks again to “AtLarge” for having done that research and letting me re-post his idea from all those years ago.

    By the way, I actually did what you tried and didn’t like, but on a KZ400. Some rubber connectors, some PVC, a single filter, and some jet adjustments. It worked pretty well, actually. Here’s a picture of it:


  7. Renoldo

    Attempting to brainstorm something like this for my KZ550, the issue that I have is that there is no viable way of fastening the moog connector onto the airbox for my particular model. If I can find the right size moog connector for the TK-26 carbs I’ll try use sealant to make it air-tight Unfortunately pods are not an option for the bike..dam CV carbs.

  8. Harvey Ganzel

    Yeah, we followed the MOOG part fix on my 1982 CSR 750 and it worked quite well. One needs to be patient when doing it, but it did the job

  9. Biquetoast (Post author)

    Thanks for the feedback!

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