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KZ400b Carbs 17 Mar 2023 08:02 #881632

  • DavidZ1R
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Hi guys, I know this subject has been discussed a good few times, my newly rebuilt engine will not idle correctly, the revs will not drop below 1800 - 2000 rpm, unless I screw the throtlle down hard. I have put the vacuum gauges on and the left is drawing alot more than the right cylinder, carbs have been rebuilt, all old jets cleaned and reused, I have even swapped over the diaphrams just to see, all the same, had the genuine new boots off and sealed on, its sounds like drawing air, but cant find where from, any ideas.

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KZ400b Carbs 17 Mar 2023 08:08 #881634

  • TexasKZ
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Have you checked to insure that the throttle cables are properly adjusted and not hanging up?
Were the carbs bench synced before installing them? one carb pulling more vacuum than the other could be because they are badly out of synch.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

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KZ400b Carbs 17 Mar 2023 08:12 #881635

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Hi Texas,  yes I have tried to sync the carbs, which ever way i go, left or right the draw on the left pot stays the same, cables are genuine and correct, I have other bikes, all Kawasaki and dont have any problems with engines, just this one.

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KZ400b Carbs 17 Mar 2023 08:43 #881637

  • Michel3007
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Have you checked that the butterfly plates are not bent?
I had this problem on my B2 and it was a bent plate. The plate could not close completely and it was as if the throttle was opened constantly, resulting in a hanging idle.

 
KZ 750 H2 LTD 1981
GPZ750R1 1982

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KZ400b Carbs 17 Mar 2023 08:59 #881639

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I whip the carbs off again and double check them, I will strip the beggars down again. 

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KZ400b Carbs 17 Mar 2023 18:29 #881659

  • Wookie58
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The vacum is highest against a closed throttle so the side with the lower readings is where your problem lies (air leak/carb issue) have you checked valve clearances and compression (vacum is created my the mechanical " suck" from the piston down stroke)

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KZ400b Carbs 17 Mar 2023 18:48 #881660

  • Scirocco
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Never ever seen a bend flaps/butterflys on carbs. Are you sure your carb sync adjuster screw or unit is installed correctly.
Some pics of the carbs/sync adjuster would help. Have seen a lot of mis-installed sync adjuster after a re-build.



 
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KZ400b Carbs 18 Mar 2023 03:25 #881666

  • DavidZ1R
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I am going to remove the carbs today, will post up pics and what I did 

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KZ400b Carbs 18 Mar 2023 03:27 #881667

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The vacum is highest against a closed throttle so the side with the lower readings is where your problem lies (air leak/carb issue) have you checked valve clearances and compression (vacum is created my the mechanical " suck" from the piston down stroke)

Yes compression great on both sides, I agree issue is with right hand carb. Will double check valves before I remove the carbs. 
 

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KZ400b Carbs 18 Mar 2023 10:00 #881688

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Right guys, checked out compressions again, all good, checked valves all good.

Removed carbs again..... Removed choke discs, emery around edges, lightly, refit screwed lightly, open and closed couple times to centre up, lock tight and screwed up tight, filled with oil to check tightness 
 

Refit carbs, checked cables. Started up and tweaked the balance 
 
success 
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KZ400b Carbs 18 Mar 2023 11:07 #881694

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Compression and vaccum sync values are perfect, don´t forget to tight and secure the sync adjuster screw and nut with a drop of screw locking paint.

 
 
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