Carb noise @ idle

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28 Jun 2011 00:46 - 30 Jun 2011 22:27 #459878 by calvin17d
Carb noise @ idle was created by calvin17d
I am adjusting my idle mixtue screw because I had a very lean midrange.... So I'm down on a knee listening to the engine turning the #1 carb screw out nice and slow and I notice a slurping noise that sounds irregular.... The noise is coming out of the pOd filter. I check the other side, and no such noise. I continue turning the screw and receive no noticeable difference in the idle at about 750 rpm. After finishing the other carbs I go for a test ride and it's now running it's best ever. I get back to the shop and yank the plugs. All plugs except #1 are uniform. One is quite rich in comparison.

Carbs syncd
Timing perfect
Valve shims dialed

Why does my bike sound like a 5 yr old quietly sipping a milk shake?

1976 Kz900 A4
Last edit: 30 Jun 2011 22:27 by calvin17d.

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  • KZ_Rage
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28 Jun 2011 16:51 #459997 by KZ_Rage
Replied by KZ_Rage on topic Carb noise idle mixture circuit
Check your float height and float seat condition

1979 KZ1000E1 SOLD!
1984 KZ550F2 SOLD!
2006 ZG1000A6F (Totaled)
2001 ZRX1200R (Sold)
2001 Sprint 955i ST (daily rider)

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30 Jun 2011 22:26 #460367 by calvin17d
Replied by calvin17d on topic Carb noise idle mixture circuit

KZ_Rage wrote: Check your float height and float seat condition


I spent several hours working the levels weeks ago. I spent some time today to double check, and all seems well. I also cleaned the idle circuit.

1976 Kz900 A4

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30 Jun 2011 22:36 #460372 by KZ_Rage
Replied by KZ_Rage on topic Carb noise @ idle
Only other thing that comes to mind is that the choke on that carb isn't sealing off the enrich pathway when you close the choke off. You could move the float and seat out of #1 to one of the other carbs, same goes for the choke assembly to see if the problem stays on #1 or follows the parts. Don't suppose you have a spare #1 carb laying around? :unsure:

Plug #1 is fluffy black or just darker?

1979 KZ1000E1 SOLD!
1984 KZ550F2 SOLD!
2006 ZG1000A6F (Totaled)
2001 ZRX1200R (Sold)
2001 Sprint 955i ST (daily rider)

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30 Jun 2011 23:09 #460378 by calvin17d
Replied by calvin17d on topic Carb noise @ idle
I dont have another carb.
The plug is darker and a little moist.
Any way to check the choke assemblies function if in fact the problem does follow it.
How do these typically fail?

Would the choke still have any influence when the bike is warm and choke disengaged?

1976 Kz900 A4

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30 Jun 2011 23:37 #460385 by KZ_Rage
Replied by KZ_Rage on topic Carb noise @ idle
The choke doesn't really "choke" it just adds more fuel to the mixture.

What carbs do you have on the bike?

Guessing they're VM26 or 28's so bare with me but there is a little plastic spool that the choke linkage engages to pull open the choke plunger and allow more fuel to pass in to the draft of the carb, if that is broken or missing then it will not work properly, also the little arm that connects it to the choke shaft common to all of the carbs might be loose or tightened down incorrectly so as not to push the plunger down all the way, if the seat/seal is not closing off properly it will continue run rich.

1979 KZ1000E1 SOLD!
1984 KZ550F2 SOLD!
2006 ZG1000A6F (Totaled)
2001 ZRX1200R (Sold)
2001 Sprint 955i ST (daily rider)

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30 Jun 2011 23:54 #460390 by TeK9iNe
Replied by TeK9iNe on topic Carb noise @ idle
You said you turned the mixture screw out, but how far? Did you properly "tune" the screws, or did you just put them at X number of turns?

Might want to actually "tune" them and then try things out.

My bike makes the slurp when its still cold/enrichener engaged some.

B)

Motorcycle Shop Owner/Operator

79 Kawie Z1000 LTD
81 Kawie Z1000 CSR
83 Honda VT750C A
85 Kawie GPZ900 A2
86 Zukie GS1150 EG
93 Yamie XV1100 E
Lucky to have rolled many old bikes through my doors ;)

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01 Jul 2011 00:38 #460398 by calvin17d
Replied by calvin17d on topic Carb noise @ idle
I was actually tuning them by starting them all the way in and listening to the engine as I backed the screw out. this was the only carb that didn't stumble when the screw was seated. I backed it out over 2 turns but never heard any difference and with the slurping noise I decided the spec'd setting would be a safe spot for a test run. The bike ran quite well after tuning but that spark plug was noticeably more rich and nearly fouled while all others were ideal in color.

1976 Kz900 A4

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01 Jul 2011 07:26 - 01 Jul 2011 07:30 #460427 by Patton
Replied by Patton on topic Carb noise @ idle

calvin17d wrote: I was actually tuning them by starting them all the way in and listening to the engine as I backed the screw out. this was the only carb that didn't stumble when the screw was seated. I backed it out over 2 turns but never heard any difference and with the slurping noise I decided the spec'd setting would be a safe spot for a test run. The bike ran quite well after tuning but that spark plug was noticeably more rich and nearly fouled while all others were ideal in color.

If turning the pilot air adjustment screw fails to influence rpm, it often indicates an imperfect pilot circuit for whatever reason, but oftentimes due to an obstructed air passage and/or an obstructed fuel passage and/or an obstructed air/fuel mixture passage, or perhaps due to a damaged pilot screw (perhaps the pointed tip is damaged or its seat - orifice - is damaged).

Where carbs are in fact clean and in otherwise perfect condition, an excessively rich pilot circuit may result from obstruction or partial obstruction of the port where air first enters the pilot circuit, this being a smaller hole located alongside the main carb bore.

Reportedly, some pods may block or partially block the pilot air entrance port, which might be a possibility with the bike at hand. Could test run without the pod on the carb to the affected cylinder to see whether it makes any difference.

Good Fortune! :)

1973 Z1
KZ900 LTD
Last edit: 01 Jul 2011 07:30 by Patton.

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01 Jul 2011 12:32 #460463 by calvin17d
Replied by calvin17d on topic Carb noise @ idle

Patton wrote: If turning the pilot air adjustment screw fails to influence rpm, it often indicates an imperfect pilot circuit for whatever reason, but oftentimes due to an obstructed air passage and/or an obstructed fuel passage and/or an obstructed air/fuel mixture passage, or perhaps due to a damaged pilot screw (perhaps the pointed tip is damaged or its seat - orifice - is damaged).
The tip seemed in okay condition. I plugged a small hose into the pilot intake and with the screw seated i could not blow air passed.

Where carbs are in fact clean and in otherwise perfect condition, an excessively rich pilot circuit may result from obstruction or partial obstruction of the port where air first enters the pilot circuit, this being a smaller hole located alongside the main carb bore.

This may have been plugged, I ran some air and cleaner through the circuit which is now passing air quite freely.

Reportedly, some pods may block or partially block the pilot air entrance port, which might be a possibility with the bike at hand. Could test run without the pod on the carb to the affected cylinder to see whether it makes any difference.

This may be something to explore. I am running K&N Pods.
Good Fortune! :)


1976 Kz900 A4

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09 Jul 2011 04:48 #461821 by calvin17d
Replied by calvin17d on topic Carb noise @ idle
Swapped valves and floats with another bowl. I also swapped the starter Plungers and still it is rich. The circuit and jets are clean.

All I can think is to swap needle jets. Do these really wear out? how do I check.

1976 Kz900 A4

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09 Jul 2011 06:40 #461823 by Patton
Replied by Patton on topic Carb noise @ idle
If needed ---



Good Fortune! :)

1973 Z1
KZ900 LTD
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