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KZ400: upgrade front suspension 08 Feb 2023 13:58 #879921

  • Feanor_twh
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I weigh 160lbs I think that's light hehe

The 11-1115 springs are lighter and are recommended for the KZ400, but the manufacturer indicates it for the GS550 (2150kg).

The serial number 11-1109 is heavier and is recommended for the KZ440, but the manufacturer indicates it for the GS400, lighter and closer in weight to the KZ400/440 (185kg)

I don't understand.
(1976) Kawasaki KZ400-D3. All original, but: electronic reg/rec (Oregon Motorcycle Parts), new handlebar controls (w/ PASS/HORN/lights switch, LED dash lights (superbrightleds.com), Dynatek coil (3ohm), MAC mufflers, HEL brake hoses, rubber fork boots, 4.00 rear tyre (Dunlop K70), chromed chainguard

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KZ400: upgrade front suspension 08 Feb 2023 17:25 #879926

  • Nerdy
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Agreed, it's not very clear.

The 11-1115 has a 30/40 spring rate (in pounds per inch, or lb/in).
The 11-1109 has a 35/45 spring rate, so it's a little heavier/stiffer.
It sounds like they have the same physical dimensions, so they can work for the 400 or the 440.

I looked at the Progressive Suspension web site and they don't list any fork springs at all - just shocks. 

The installation manual PDF on Dennis Kirk for the 11-1109 seems to be for Goldwings: it references GL1000, GL1200, and GL1500. It also references a chart that is not actually part of the document.

I think you would be fine with either set of springs and making adjustments in the fork oil type.
 
1979 KZ400 Gifted to a couple of nephews
1967 Yamaha YCS1 Bonanza
1980 KZ440B
1981 Yamaha XT250H
1981 KZ440 LTD project bike
1981 GPz550
2013 Yamaha FZ6R
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KZ400: upgrade front suspension 09 Feb 2023 10:14 #879941

  • Feanor_twh
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I already ordered the 11-1109. As we say here, "ante la duda, la más tetuda" haha

The reviews on Amazon were good too, someone even talked about a KZ400.

Thanks for the advice and for your time, mate. When I have assembled them I will post reviewing the result.
(1976) Kawasaki KZ400-D3. All original, but: electronic reg/rec (Oregon Motorcycle Parts), new handlebar controls (w/ PASS/HORN/lights switch, LED dash lights (superbrightleds.com), Dynatek coil (3ohm), MAC mufflers, HEL brake hoses, rubber fork boots, 4.00 rear tyre (Dunlop K70), chromed chainguard

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KZ400: upgrade front suspension 09 Feb 2023 15:28 #879967

  • Nerdy
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You're very welcome - not sure how helpful I was though. And that saying is definitely a good one. :-)

It would be good to see the results. Thanks!
1979 KZ400 Gifted to a couple of nephews
1967 Yamaha YCS1 Bonanza
1980 KZ440B
1981 Yamaha XT250H
1981 KZ440 LTD project bike
1981 GPz550
2013 Yamaha FZ6R

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KZ400: upgrade front suspension 23 Feb 2023 05:05 #880668

  • Feanor_twh
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I mounted the 11-1109 springs. The fork is fully extended with the empty weight of the bike, and it sags a bit when you sit on it. Dive under braking has been decreased considerably and overall the feel is stiffer (maybe too much, but I prefer that to diving).

Original springs measure 475mm. The new ones are 500, which adds a significant amount of preload and made it nearly impossible to bolt on the top plugs. But with the 11-1115 (softer) springs this would be exactly the same.

Happy overall. I doubt there is a better option for this bike today.
(1976) Kawasaki KZ400-D3. All original, but: electronic reg/rec (Oregon Motorcycle Parts), new handlebar controls (w/ PASS/HORN/lights switch, LED dash lights (superbrightleds.com), Dynatek coil (3ohm), MAC mufflers, HEL brake hoses, rubber fork boots, 4.00 rear tyre (Dunlop K70), chromed chainguard
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KZ400: upgrade front suspension 14 Mar 2023 16:43 #881520

  • Sdaniels2010
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I mounted the 11-1109 springs. The fork is fully extended with the empty weight of the bike, and it sags a bit when you sit on it. Dive under braking has been decreased considerably and overall the feel is stiffer (maybe too much, but I prefer that to diving).

Original springs measure 475mm. The new ones are 500, which adds a significant amount of preload and made it nearly impossible to bolt on the top plugs. But with the 11-1115 (softer) springs this would be exactly the same.

Happy overall. I doubt there is a better option for this bike today.
Most manufacturers specify a specific spring preload but if your new springs are 25mm longer you would likely need to shorten your spacers...probably why you had some difficulty with the top plug.  
1981 KZ440 A2 LTD

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