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Jet needle improves acceleration. 16 Jul 2011 21:34 #463224

  • calvin17d
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Well my special order on the pilot jets still has not arrived from the local shop. Ordering from Z1e hAs been more efficient.

Meanwhile I pulled the needle and put them back to stock position, after which I also mechanically syncd them. A test drive quickly revealed how the added fuel from raising the needle had helped so much. I was unable to achieve smooth operation but made the needle change in preparation of the larger pilots. I had previously used a home
Made sync kit to sync the carbs before all this needle swapping. It must have worked well as the bike has not ran this poorly in over a month. It may be time for vacuum gauges. I am quickly pissing my summer away. Any recommendations on a decent set that won't require a half months pay?

One other thing to note. My # 1 carb continues to run rich and is not influenced by seating the air screw. I have the pod filters off. Covering the intake for the pilot on all other carbs nearly kills the bike but doing so on #1 does nothing. Could this be sync related. I have verified clear pilot circuit by covering the air intake, the mix screw and pilot jet holes while blasting carb cleaner through. I alternated different hole plugging and spraying combinations at each hole and all were clear. I have also interchanged jets, needle valves and the choke plunger with no improvement in mixture response???? could this be a poor sync?
1976 Kz900 A4

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Jet needle improves acceleration. 16 Jul 2011 22:53 #463239

  • Patton
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calvin17d wrote: ... # 1 carb continues to run rich and is not influenced by seating the air screw....


Seating the screw is the richest position.

Good Fortune! :)
1973 Z1
KZ900 LTD

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Jet needle improves acceleration. 16 Jul 2011 23:04 #463243

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I understand that. Allow me to clarify.
After cleaning with carb fluid thru the pilot jet hole, the idle air intake hole, and also thru the mixture screw hole and achieving carb cleaner spray thru the pilot circuit into the bore, I am still rich at idle on that one cylinder with the screw at 2-1.5 turns out. If I slowly turn the screw to seat and back out there is no change in idle. The other cylinder will nearly kill the engine when I do this.

I Am aware that this indicates an obstruction in the pilot circuit. Are there any other legs Of the circuit I did not mention above? I have cleaned 3 times the items listed Above.
1976 Kz900 A4

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Jet needle improves acceleration. 16 Jul 2011 23:35 #463247

  • Patton
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Sounds like the pilot circuit passages are clean.

And let's presume that the pilot jet is the correct size and in good condition and that the holes in the pilot jet are clear and have not been enlarged by over zealous cleaning.

What the heck, let's presume that the pilot circuit is perfect.
But still producing a too rich fuel mixture.

One reason might be a too high fuel level.

Another reason might be an imperfect enrichener circuit function which could be due to some malfunction of the choke plunger.

Yet another reason might be a dirty or obstructed pod filter (if pods are fitted), or possibly the pod rubber is partially blocking the pilot air entrance hole (as some less expensive pods are reportedly prone to do).

For the benefit of other readers, please see below for the pilot circuit cleaning method to which I believe you're referring.

Good Fortune! :)


1973 Z1
KZ900 LTD
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Jet needle improves acceleration. 16 Jul 2011 23:43 #463250

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calvin17d wrote: I understand that. Allow me to clarify.
After cleaning with carb fluid thru the pilot jet hole, the idle air intake hole, and also thru the mixture screw hole and achieving carb cleaner spray thru the pilot circuit into the bore, I am still rich at idle on that one cylinder with the screw at 2-1.5 turns out. If I slowly turn the screw to seat and back out there is no change in idle. The other cylinder will nearly kill the engine when I do this.

I Am aware that this indicates an obstruction in the pilot circuit. Are there any other legs Of the circuit I did not mention above? I have cleaned 3 times the items listed Above.


I it possible that your float hight is too high? Just a thought.
Kenny Hicks
74 Honda CB550
75 Honda CB360 (runs and rides good but not a show bike)
77 KZ650B1 (Runs Great, but needs painted and a little work.)

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Jet needle improves acceleration. 17 Jul 2011 00:00 #463254

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Patton wrote: Sounds like the pilot circuit passages are clean.

And let's presume that the pilot jet is the correct size and in good condition and that the holes in the pilot jet are clear and have not been enlarged by over zealous cleaning.

What the heck, let's presume that the pilot circuit is perfect.
But still producing a too rich fuel mixture.

One reason might be a too high fuel level.

Another reason might be an imperfect enrichener circuit function which could be due to some malfunction of the choke plunger.

Yet another reason might be a dirty or obstructed pod filter (if pods are fitted), or possibly the pod rubber is partially blocking the pilot air entrance hole (as some less expensive pods are reportedly prone to do).

For the benefit of other readers, please see below for the pilot circuit cleaning method to which I believe you're referring.

Good Fortune! :)



Fuel level was set below spec to troubleshoot this problem with no positive results.

This problem exists with pod filters removed.

I had also swapped the choke plunger with my most lean cylinder and found no change.
1976 Kz900 A4

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Jet needle improves acceleration. 17 Jul 2011 00:30 #463259

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calvin17d wrote: Fuel level was set below spec to troubleshoot this problem with no positive results.
This problem exists with pod filters removed.
I had also swapped the choke plunger with my most lean cylinder and found no change.


If not already done, could swap #1 pilot screw with another carb's screw to see whether that makes any difference in #1 richness.

If no change, could swap #1 pilot jet with another carb's jet to see whether that makes any difference in #1 richness.

The idea here being to rule out possible pilot screw damage or pilot jet damage.

Is the rubber pad on bottom of #1 choke plunger in good condition?
If worn or missing, might allow fuel from enrichener even with plunger closed.
Edit -- I see that's already been considered.

Good Fortune! :)
1973 Z1
KZ900 LTD

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Jet needle improves acceleration. 17 Jul 2011 00:36 #463264

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Patton wrote:

calvin17d wrote:

Fuel level was set below spec to troubleshoot this problem with no positive results.
This problem exists with pod filters removed.
I had also swapped the choke plunger with my most lean cylinder and found no change.


If not already done, could swap #1 pilot screw with another carb's screw to see whether that makes any difference in #1 richness.

If no change, could swap #1 pilot jet with another carb's jet to see whether that makes any difference in #1 richness.

The idea here being to rule out possible pilot screw damage or pilot jet damage.

Is the rubber pad on bottom of #1 choke plunger in good condition?
If worn or missing, might allow fuel from enrichener even with plunger closed.

Good Fortune! :)


Have swapped floats, main jets, pilot jets, needle valves and seats, mixture screws, and an entire plunger including the rubber boot.

No effect.

Keep the ideas rolling.

1976 Kz900 A4

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Jet needle improves acceleration. 17 Jul 2011 00:38 #463265

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What's the effect on #1 if tested with the pilot screw completely removed?
Still too rich?
1973 Z1
KZ900 LTD

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Jet needle improves acceleration. 17 Jul 2011 00:42 #463266

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May be nearing time to swap #1 and #2 carbs to see whether the richness issue follows the #1 carb when it's feeding #2 cylinder.

Perhaps already covered, but is there good spark on both #1 and #4 plugs?
1973 Z1
KZ900 LTD

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Last edit: by Patton.

Jet needle improves acceleration. 17 Jul 2011 01:22 #463274

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Visually spark seems fat across the board. Ruling this out would be silly and looking troubleshooting electrical would not be my strong suit. Recommended checks and their procedures would be a great help.
1976 Kz900 A4

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Jet needle improves acceleration. 17 Jul 2011 09:51 #463309

  • DoubleDub
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Three things I can think of to check regarding spark:

1. Resistance (ohms) of the spark plug boots (cheap to replace if bad and they screw on and off)
2. Resistance (ohms) of the coils (the manual has the procedure, there are two measurements you need to take - Z1Enterprises has replacement coils that are very reasonable in price).
3. Voltage being received at the coils when the ignition is on (indication of other wiring issues creating lower than optimal voltage feeding the coils).

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