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Author Topic: 2 cylinders rich, 2 cylinders lean  (Read 1052 times)

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Offline boaf

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2 cylinders rich, 2 cylinders lean
« on: May 28, 2018, 02:07:43 PM »
I am having an issue with cylinder 1/4 running rich and 2/3  running lean-ish. 

The following maintenance items have been done.

Cam chain adjustment
Valve adjustment
Complete carb cleaning when rebuilt 500 km ago.
Float heights checked with clear tube
Timing set
Carbs synched

Plugs: X24ESR-U
Intake: Cognito Moto Airbox
Exhaust: Hindle 4-2-1

Carb settings:

Model: PD46C
Main: #105
Slow: #42
Needle: Middle (3rd) - stock was 2nd from top
Float: 14.5mm
Mixture: 1.5 turns


Bike runs and idles well and easily pulls to redline and up to speed but the plugs just don't look right.

Should I be looking at plug caps, carb boots/clamps or something different?



« Last Edit: May 28, 2018, 04:33:43 PM by boaf »
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Offline boaf

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Re: 2 cylinders rich, 2 cylinders lean
« Reply #1 on: May 29, 2018, 07:20:52 AM »
Thanks. I’ll swap the coils and see if the issue follows.  I have a replacement set of points and condensers but they are not OEM so was hoping to not use them.

I was thinking it might be a carb boot/clamp issue too. Accordingly to some stuff I read, if a cylinder is rich the previous one in the firing order could be lean.

If I can get all 4 cylinders to read the same, no matter how they read, that would be ideal.  Then the proper tuning can be done.

Attached is a photo of what I’m calling lean.  On a second look it actually looks pretty good?
« Last Edit: May 29, 2018, 07:22:39 AM by boaf »
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Offline david 750f

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Re: 2 cylinders rich, 2 cylinders lean
« Reply #2 on: May 29, 2018, 07:25:13 AM »
Thats not a lean plug. I would say good to slightly rich. Post some photo's of all the plugs.
« Last Edit: May 29, 2018, 07:38:44 AM by david 750F »
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1976 CB 750F

Offline boaf

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Re: 2 cylinders rich, 2 cylinders lean
« Reply #3 on: May 29, 2018, 12:04:09 PM »
Quote from: david 750F on May 29, 2018, 07:25:13 AM
Thats not a lean plug. I would say good to slightly rich. Post some photo's of all the plugs.

No change after swapping coils.

Plugs are 1-4 left to right. Closeups are 1/4 and 2/3.

Going to double check for vac leaks and then swap condensers/points.
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Offline boaf

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Re: 2 cylinders rich, 2 cylinders lean
« Reply #4 on: May 29, 2018, 12:33:45 PM »
I’m on it.

I’ll warm it up on old plugs.

Have it done about about 7:30 EST and will report. Have to get the kids from school now.

Thanks.
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Offline boaf

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Re: 2 cylinders rich, 2 cylinders lean
« Reply #5 on: May 29, 2018, 04:13:50 PM »
Warmed up on old plugs.

Fresh plugs, 3 minute idle.  Only #4 shows any colour.

Waiting to get my hands on my multimeter to test plug cap and coil resistance.  Should have it done shortly.
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Offline david 750f

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Re: 2 cylinders rich, 2 cylinders lean
« Reply #6 on: May 29, 2018, 06:19:22 PM »
Boaf, I see your in Canada. What gas are you running? I’m in Toronto. Try some Shell Supreme, no ethanol.. it helps with the plug tuning.. Esso preimium is the same gas
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1976 CB 750F
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