Different size main jets

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04 Mar 2022 16:24 #863205 by Mtl1000
Different size main jets was created by Mtl1000
Just wondering why the jet sizes decreased over time on the 28mm mikuni , is it because of emission laws ?
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04 Mar 2022 16:53 #863207 by krazee1
Replied by krazee1 on topic Different size main jets
I think the carbs other than the Z1R were 26mm after 1975, the chart you pictured shows that.  I believe the 28ss carbs in 1980 were the ones with accelerator pumps?, possibly did not need as much main jet.  Emissions laws came into effect  for the 1978 model year motorcycles IIRC.  

Mike
Former M.E. at Kawasaki Motors Manufacturing, Lincoln, NE
1966 W1 (the Z1 of 1966-50H.P. and 100mph!)
1974 Z1
1978 KZ1000 LTD
1976 KZ900B pile O parts
1980 KZ750E
1980 Honda XL250S (I know, wrong flavor!)
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04 Mar 2022 18:25 - 04 Mar 2022 19:30 #863209 by Mikaw
Replied by Mikaw on topic Different size main jets
It’s not just the main that affect performance. Cutaway and needles are different. They could have moved the sweet spot to a different rpm to gain as much performance within the tightening fuel economy requirements. 
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.
Last edit: 04 Mar 2022 19:30 by Mikaw.
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  • hardrockminer
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04 Mar 2022 19:22 #863211 by hardrockminer
Replied by hardrockminer on topic Different size main jets
The main reason was emissions and mainly at idle.  
I have several restored bikes along with a 2006 Goldwing with a sidecar. My wife has a 2019 Suzuki DR 650 for on and off road.
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