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hanging idle, no leaks... 27 Mar 2017 17:00 #757881

  • Scirocco
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Yes,this sucks but somewhere in your carb system is an air leak.

I have a friend with a Suzuki 800 Intruder with the same problem,i try everything to get
the bike run well at idle,nothing helps. I was totally confused.
At last It turned out that the shaft of the butterfly's ( or Carb body bore ) at this point was totally worn and cause an air leak.
After a we changed the complete carb body with an other used one all got well!
Sync the carbs and choke mechanism on this bike is a real challenge, trust me.

Michael
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Last edit: by Scirocco.

hanging idle, no leaks... 27 Mar 2017 20:10 #757906

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shamal wrote: ...
Vacuum synch are showing 16cm hg in all 4 carb....

Any unusual differences among the pilot screw settings?

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1973 Z1
KZ900 LTD

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Last edit: by Patton.

hanging idle, no leaks... 28 Mar 2017 03:31 #757922

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Patton wrote:

shamal wrote: ...
Vacuum synch are showing 16cm hg in all 4 carb....

Any unusual differences among the pilot screw settings?

Good Fortune! :)


no. they are set 2 1/2 turns now but if i try to move the screw the hang idle is still here.
how a electronic ignition can fail and change the timing?
the last thing that remain it's a shaft leak on the carbs, even if i can't find it.
i'm out of ideas.
since the problem become worse when warm i tend to exclude a exhaust leak.
valve clearance it's done.
i have all stock except the mufflers : they are two marving replica of the OEM mufflers.
can be the exhaust too restricted? causing some back pressure? i really don't know.


EDIT
i talked with a eletronic techinician. he say the 34 years old electrolitic condensers inside the CDI box can still work , but he is SURE they are pretty dry and for SURE does not work so well...
in any words: a cdi can keep sparking but maybe some parameters can change.
i think it's time to try another CDI..
and at all the problem was present before the new boots and rebuilded carbs. ..
the bike is showing the same, identical, sympthoms as before.
1983 kz 550 h

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Last edit: by shamal.

hanging idle, no leaks... 28 Mar 2017 08:22 #757946

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650ed wrote: If you haven't already done so, try this -

Disconnect the throttle cables at the carbs. The start the bike and give it some revs by manipulating the throttle at the carbs using your hand. If the revs still hang you have ruled out the cables and throttle grip as a possible problem. If the revs still hang you have identified the problem which should be easy to correct by lubing the cables and throttle grip. Ed


This.

I'd disconnect the throttle cable(s) to eliminate the control. If you haven't found the issue yet, you need to narrow down options. You're not adjusting the idle by the cable, right? Is there proper freeplay in the throttle adjustment? Is the end of the grip rubbing on the handlebar? Is the throttle housing clean?
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2004 KX125
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hanging idle, no leaks... 28 Mar 2017 09:24 #757950

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Of course i don not use the cable to adjust the idle. I use the knob
Cable is not the problem, i have no more possibile freeplay but i have at least 2 mm of freeplay. When i shut the gas off the butterflies snap return with the "TACK" sound.
Whats your thoughts about my post above about ignition?
1983 kz 550 h

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hanging idle, no leaks... 28 Mar 2017 10:14 #757952

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I've seen MANY times people adjusting the idle with the throttle cable.

Since you haven't found anything yet, I would disconnect the throttle cable to be 100% sure it's not the culprit. Has the bike ever run properly before? In my experience, CDI's either work or don't.

Those carbs have diaphragm slides, one could be sticking. Try spraying the slides with WD and see if it still hangs.
1975 Z1 900
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2004 KX125
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hanging idle, no leaks... 28 Mar 2017 11:20 #757955

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Kidkawie wrote: I've seen MANY times people adjusting the idle with the throttle cable.

Since you haven't found anything yet, I would disconnect the throttle cable to be 100% sure it's not the culprit. Has the bike ever run properly before? In my experience, CDI's either work or don't.

Those carbs have diaphragm slides, one could be sticking. Try spraying the slides with WD and see if it still hangs.


slides are not sticky, i have just finished rebuild the carburetors.
i will try disconnect the cable but i think if a cable it's sticky when engine is hot, it should be sticky even when engine is cold.
when cold the rpm drop quick..
in the cARBURETORS all it's moving free. all new lines and oring as i said above :/. the bike is doing this thing since i bought her. all the new components in the intake system, igniton coils, wires, boots, plug and caps.. etc etc and she is still doing the same identical thing!!!!
CDI can fail too, as i read on the web.
:( uff
1983 kz 550 h

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hanging idle, no leaks... 29 Mar 2017 03:16 #758003

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Im going to check again after i triple checked it my cam timing when i changed the cam chain. I tought this low vacuum reading while synching (14cm hg) and the hot engine hang idle can be fault of a tooth of on the cams.
Im pretty sure the cam timing its ok , but i want to check it again.
If the engine is a tooth of on one cam, will be the engine so easy to start , cold or hot? Will be the bike so plenty of power? I really dont know if a single tooth off can make the engine hard to start or something. All i can say is the bike on the road its fast , responsive under load, and can reach 100 mph in a bit...
1983 kz 550 h

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hanging idle, no leaks... 29 Mar 2017 14:31 #758053

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It might be helpful to determine whether one particular carb is responsible for causing the momentary "racing" idle following throttle closure.

When the throttle is lightly blipped during running sync, do the gauges remain equal during the momentary "racing" idle following throttle closure? An obvious gauge vacuum difference during the momentary "racing" idle might help toward determining whether one particular carb is responsible for causing the condition.

If the engine is able to "idle" on 3 cylinders when #4 spark plug is removed and laid grounded against the engine head so it can spark (to complete the secondary loop) -- In this test configuration, does the momentary "racing" idle following throttle closure persist? Same test results with only #3 spark plug removed? Only #2 plug removed? Only #1 removed?

This is making me fall in love with my manual slide Mikuni carbs all over again. :lol:

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1973 Z1
KZ900 LTD
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Last edit: by Patton.

hanging idle, no leaks... 29 Mar 2017 15:15 #758054

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I have to perform this and i let you know.
The awesome thing about vacuum leaks is that i unplugged a vacuum caps while engine was running and nothing change. With a hell of a vacuum leak like this the engine was LOSING RPM, instead of go higher. How its possible to explain this?
Anyway, i think the valvevtiming its ok. Can a 228kg bike do power wheelie with a tooth off on the intake cam? Mh..
PATTON, tell me. What about the way to determinate if my slide valves springs are worn?
The slides does not snap return extremly fast. But they are free and does not stick.
1983 kz 550 h

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hanging idle, no leaks... 29 Mar 2017 18:33 #758073

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At least for a test, perhaps some added initial compression could be achieved by placing a washer or two (or maybe an o'ring) at one end of the springs before fitting the springs.

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1973 Z1
KZ900 LTD
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Last edit: by Patton.

hanging idle, no leaks... 29 Mar 2017 18:49 #758076

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Another test --- If set idle speed adjustment slightly too low (to where the engine dies) --- when the throttle is blipped, does the momentary "racing" idle appear before the engine dies?

Good Fortune! :)
1973 Z1
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Last edit: by Patton.
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