1975 KZ400 sticky throttle

  • madmatt1
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1975 KZ400 sticky throttle

24 May 2011 22:24
#453370
I just rebuilt my carbs, which of course included a thorough cleaning. I used simple green
as a cleaning solution. The bike is back together and runs well, but the engine is now very
slow to idle back down after revving. Coming to a stop I often have to fidget with the throttle
to get it to go back to the proper idle speed. The carbs are Keihin CVB36, with solid pistons, not
the rubber diaphragm type. I lightly oiled the slides before reassembly as well. Is it possible that
the walls of the carbs are sticky? What else might I have overlooked?
1977 KZ1000 LTD
1979 KZ1000 LTD
1978 KZ1000A

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  • Treewizard
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Re: 1975 KZ400 sticky throttle

24 May 2011 22:39
#453376
i would replace the carb holders, espically if they r stock, thats the most common place to have a vacume leak (not returning ti idle)

adjusting the idle down will help with that also

secondly id make sure the throttle cable is both lubricated properly and that its not binding internally

good luck!
1983 KZ 750 shaft
2002 ZRX 1200R
Raleigh NC

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  • Patton
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Re: 1975 KZ400 sticky throttle

24 May 2011 23:21
#453388
madmatt1 wrote: ...lightly oiled the slides before reassembly as well....

Imo, the slides should not be oiled, and the carb internals should be reassembled completely dry.

Good Fortune! :)
1973 Z1
KZ900 LTD

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  • Patton
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Re: 1975 KZ400 sticky throttle

24 May 2011 23:24
#453392
Might be able to remove the oil by removing the carb top covers and spraying carb cleaner down around the slides while working the throttle.

Good Fortune! :)
1973 Z1
KZ900 LTD

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  • 650ed
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Re: 1975 KZ400 sticky throttle

24 May 2011 23:26
#453393
Patton wrote:
madmatt1 wrote: ...lightly oiled the slides before reassembly as well....

Imo, the slides should not be oiled, and the carb internals should be reassembled completely dry.

Good Fortune! :)

+1 Another issue is that the oil may tend to attract and hold dirt that can cause binding. Ed
1977 KZ650-C1 Original Owner - Stock (with additional invisible FIAMM horn)

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  • madmatt1
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Re: 1975 KZ400 sticky throttle

25 May 2011 01:20
#453415
I'll give that a try- it's so easy to take the tank off the bike I'll just pull the tops off and take the slides out and clean em' off with Carb clean. I have just read other forums where guys said to put a thin layer of light oil on the slides. Didn't check the carb holders for leaks- they look pretty fresh and are soft...but I'll give them the spray test anyhow. I know it's not the cables-I already went over them.... plus it does the same thing even when you manually control the carbs. The other thought I just had is that maybe the advancer isn't returning. I haven't checked this yet or taken the plate off- but I've had the cover off and all the components are clean and new looking so I didn't tear it down. Maybe tomorrow.
1977 KZ1000 LTD
1979 KZ1000 LTD
1978 KZ1000A

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  • hoghaterkaw
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Re: 1975 KZ400 sticky throttle

25 May 2011 11:21
#453464
All the advice given so far is good. You said cables, so here is what I would first. Make sure you have enough slack on the throttle return cable. Too little slack on the return cable will cause the cables to bind and not return to idle.

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  • loudhvx
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Re: 1975 KZ400 sticky throttle

25 May 2011 14:38 - 25 May 2011 14:40
#453497
I haven't seen CV36's work without at least 1 drop of oil on the wide part of the piston slides, and the center tube. Without it they bind up and restrict power.

Also critical is tightening the upper covers precisely. You have to do it with the carbs in their normal orientation (slides vertical). You just very lightly tighten the screws and alternate a little bit more torque on each side while simulataneously reaching in and actuating the slides up and down manually. This way the caps get tightened down while centered. If not, they will bind.

When done properly, both slides will drop simultaneously and will make a single bottoming sound. If you hear two clicks, then one is being delayed for some reason.

(good idea to check the advancer)
1981 KZ550 D1 gpz.
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Last edit: 25 May 2011 14:40 by loudhvx.

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  • Kidkawie
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Re: 1975 KZ400 sticky throttle

25 May 2011 15:29
#453503
Remove the return cable, that will eliminate that. Make sure the slides "snap" back to idle. An improprerly routed cable might do that too.
1975 Z1 900
1994 KX250 Supermoto
2004 KX125

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  • Patton
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Re: 1975 KZ400 sticky throttle

25 May 2011 17:13
#453519
loudhvx wrote: I haven't seen CV36's work without at least 1 drop of oil on the wide part of the piston slides, and the center tube. Without it they bind up and restrict power.

Also critical is tightening the upper covers precisely. You have to do it with the carbs in their normal orientation (slides vertical). You just very lightly tighten the screws and alternate a little bit more torque on each side while simulataneously reaching in and actuating the slides up and down manually. This way the caps get tightened down while centered. If not, they will bind.

When done properly, both slides will drop simultaneously and will make a single bottoming sound. If you hear two clicks, then one is being delayed for some reason.

(good idea to check the advancer)

Thanks, lou! :cheer:

Reading info like this makes me learn to hate CV carbs all over again. :laugh:
1973 Z1
KZ900 LTD

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  • hoghaterkaw
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Re: 1975 KZ400 sticky throttle

25 May 2011 17:31
#453522
Here is a link from the past that is food for thought.

www.kzrider.com/archive/viewthread.php?tid=23668&page=1

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  • Patton
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Re: 1975 KZ400 sticky throttle

25 May 2011 17:45
#453525
click > www.kz400.com/Workshop%20manual%20bilder/CV%20Carbs.pdf

Good Fortune! :)
1973 Z1
KZ900 LTD

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