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!982 GPZ750 forks 22 Jun 2022 15:32 #869221

  • 750 R1
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I put my GPZ750 forks on my sons 1982 KZ650,it is a straight swap, the problem is that they don't hold air.  They have new seals and have no oil leaks but i put 12 PSI in them and in a couple of hours they leak down to about 4 PSI and forks are really soft. I need to add some preload spacers and was wondering if anyone here has done it, and if so, what length spacers were used ?  Are there longer springs that can be used ?   Just weighing up all options...

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!982 GPZ750 forks 22 Jun 2022 16:41 #869223

  • Nessism
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You might want to some new (stiffer) springs.  There are various options in the USA, but not sure where you are at.  The air assist was all the rage during the KZ era, but it died quickly for reasons like you mention (not holding air, and increased seal stiction.)  

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!982 GPZ750 forks 22 Jun 2022 18:13 #869228

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You might want to some new (stiffer) springs.  There are various options in the USA, but not sure where you are at.  The air assist was all the rage during the KZ era, but it died quickly for reasons like you mention (not holding air, and increased seal stiction.)  


I'm in Australia.  Yes,I've considered stiffer springs but I have noway of knowing if they are still supposed to work with the air in fork system, no use buying new springs if they also need air, hence the spacer route. Also,cost of shipping from the USA at the moment is stupid high...

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!982 GPZ750 forks 22 Jun 2022 19:05 #869230

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You might want to some new (stiffer) springs.  There are various options in the USA, but not sure where you are at.  The air assist was all the rage during the KZ era, but it died quickly for reasons like you mention (not holding air, and increased seal stiction.)  


I'm in Australia.  Yes,I've considered stiffer springs but I have noway of knowing if they are still supposed to work with the air in fork system, no use buying new springs if they also need air, hence the spacer route. Also,cost of shipping from the USA at the moment is stupid high...

I installed Sonic Springs in my 750.  They offer several spring rates, so you can select based on your need, and you don't need to monkey around with the air.
Bummer about shipping.  I feel for you on that.

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!982 GPZ750 forks 22 Jun 2022 20:13 #869232

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Thanks Ed.  I was just checking out sonic springs ,they don't have a listing for the 750 R1, Do you know what other model used the same forks at all, or were they a one off like the 750R1 itself ? 
Also, are those springs rated as stand alone springs or are they still rated to be used with air ?  I suppose I'll have to weigh the bike to get accurate info for the springs, I do like a little firmer than stock...

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!982 GPZ750 forks 22 Jun 2022 20:43 #869236

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I just installed Sonic springs in my 80 E1. Pretty easy. You need to find the static installed length and then you cut the supplied pvc spacer to get the recommended preload. Then you add fork oil to the Sonics specs. The air system is completely eliminated. Here is their tech help email address. This email address is being protected from spambots. You need JavaScript enabled to view it.
1976 KZ 900 A4 kzrider.com/forum/11-projects/613548-1976-kz-900-a4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.
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!982 GPZ750 forks 22 Jun 2022 23:31 #869237

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I installed Sonic spring on my bike as well and it stiffened up the front really nicely. I was debating between Sonic and Race Tech but went with sonic. If you go to Race Tech website, they have nice spring calculator and I went with the spring rate based on that. With my weight and the type of riding, I think mine was the 0.90/kg rate spring. And yes, it comes with spacer you need to cut it.

Of course, my bike is still on the process so no riding yet but when you move around the bike, it has a nice feel to it , specially when you grab the front brake.
82' KZ750-R1 cafe racer style. Clip-on, Rear set, Fork-Brace, Mikuni Flat-slide (forgot the size), Kerker.
84' GPz750 (basket case). everything are in pieces.
89' ZX750-H1 (ZX-7 Ninja). Resurrection project are on going with my KZ750. Everything is stock.
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!982 GPZ750 forks 23 Jun 2022 01:03 #869239

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Thanks Fellas. I've done a bit of reading today and worked out  the sonic and racetech  springs eliminated the outdated air system, I should have realised straight away from the spring rates, a bit of brain fade there...  I think I'll cut some spacers for the time being then order some new springs...  Just as well this is my sons bike, I found all sorts of goodies I'd probably buy if it was mine...!!!
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