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Rejetting carbs after major work 20 Aug 2021 18:27 #854116

  • rokit_armor
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These silly CV carbs are going to be the death of me. 
Rebuilt my motor, and now I can't get the dang thing to little more than fire a couple times.
The specs:
KZ1100 A2
75mm bore 10.25:1 wiseco pistons (K1171 kit)
Web 110 cams
MAC 4-in-1 exhaust - with ceramic baffling added
Pods on intake (I know, I know)
BS34s with 137.5 mains, 45 pilots w/pilot screw 3.5 out - this is how it was jetted before the bore/cam work was done and ran just fine like this. I have also moved 300' up in elevation since it last ran, if that makes a difference.

Head has been done with new valves, properly shimmed. Timing is set correctly.

With the cam and high compression pistons, would one tend to need to go richer, or leaner?
I would suspect richer, however the plugs are black, potentially wet. 
I rejetted to 125 and 40 pilots, no change. 
Restricted airflow in pods, no change.

I forgot to plug the vacuum nubs up once, and it kinda fired up, which confuses me.

Thanks for any advice guys, always appreciate it.

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Rejetting carbs after major work 20 Aug 2021 20:57 #854123

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I decided to take a step back and start troubleshooting from the beginning. Cam timing is good. I have spark on all four plugs (New wires, original coils, I did not use the stock plugs, will this be an issue?) however it is doing a strange thing where it fires about 30 degrees advanced and then again on time, it doesn't do it all the time, I'd say about every 5 or so rotations. Is this an issue?

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Rejetting carbs after major work 21 Aug 2021 04:05 #854129

  • Rick H.
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I am not sure what setup you have, but it sounds like your spark advancer could be the problem if your ignition system is similar to a 900/1000.  If the weights are sticking timing will be advanced when it shouldn't be.  Others will chime in that may have an engine like yours.  There are some more detailed threads on this subject, but a defective timing advancer can give you fits.

Rick H.
Rick H.

1977 Kawasaki KZ-1000A1

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Rejetting carbs after major work 21 Aug 2021 04:55 #854132

  • slmjim+Z1BEBE
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Did you check compression?  What is the voltage at the coil primaries?

Higher compression requires higher potential (spark energy/voltage) for the spark to cross the plug gap.

For practical purposes, atmosphere is an insulator.  High voltage is required to ionize atmosphere at standard sea level pressure enough to become conductive, allowing a spark to cross a gap.  The larger the gap, the higher the voltage required to create enough ionization to allow the atmosphere to conduct, resulting in a spark.

When atmosphere is compressed, it's insulating properties increase, requiring more voltage to create a spark than at normal atmospheric pressure.  The higher the compression, the more voltage is required to spark across the same gap.

Stock coils are notoriously average, at best.  Stock coils that were adequate for stock compression might not be powerful enough to reliably spark the plugs at higher compression.

You might consider installing more powerful coils to go along with the higher compression.

Good Ridin'
slmjim & Z1BEBE
A biker looks at your engine and chrome.
A Rider looks at your odometer and tags.

1972 Z1 x2
1974 Z1-A x2
1975 Z1-B x2
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Rejetting carbs after major work 21 Aug 2021 08:16 #854142

  • Mikaw
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Did you check compression?  What is the voltage at the coil primaries?

Higher compression requires higher potential (spark energy/voltage) for the spark to cross the plug gap.

For practical purposes, atmosphere is an insulator.  High voltage is required to ionize atmosphere at standard sea level pressure enough to become conductive, allowing a spark to cross a gap.  The larger the gap, the higher the voltage required to create enough ionization to allow the atmosphere to conduct, resulting in a spark.

When atmosphere is compressed, it's insulating properties increase, requiring more voltage to create a spark than at normal atmospheric pressure.  The higher the compression, the more voltage is required to spark across the same gap.

Stock coils are notoriously average, at best.  Stock coils that were adequate for stock compression might not be powerful enough to reliably spark the plugs at higher compression.

You might consider installing more powerful coils to go along with the higher compression.

Good Ridin'
slmjim & Z1BEBE
Thank you for explaining this, I had heard the same thing but never an explanation of why. This is such a great forum. 
1976 KZ 900 A4 kzrider.com/forum/11-projects/613548-1976-kz-900-a4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.

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Rejetting carbs after major work 21 Aug 2021 09:47 #854147

  • rokit_armor
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No eBay APP ID and/or Cert ID defined in Kunena configurationGreat explanation, thank you so much! 
I'll double check the advancer, just in case its sticking.
Anyone have a set of green Dyna coils they'd be willing to part with?

So the plan should be as follows- 
Upgrade coils
Jet to stock, and jet up until powerband is good?

Edit: Has anyone had good luck with Magna coils? The price point is a bit more reasonable for me. 

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Last edit: by rokit_armor.

Rejetting carbs after major work 21 Aug 2021 13:20 #854155

  • DoctoRot
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if the system remains the same and only compression or displacement changes you will typically need to jet leaner. the engine is creating a  stronger signal to the carbs by breathing more and faster so it draws too much fuel. if it wants to run without the vacuum plugs in that would suggest that it is very rich.

have you verified you're getting full voltage to coils?

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Last edit: by DoctoRot.

Rejetting carbs after major work 21 Aug 2021 17:56 #854160

  • rokit_armor
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I checked a few things:
  • primary coil ohms at 3 ohms
  • Secondary at 12k ohms
  • Pickups are at 450 ohms 
Voltage at the primary coil was low, 11.5 ohms vs 13 at the battery. Cleaned a few of the connections and got it up to 12.1.  Half of the old plastic connectors are deteriorating and there is a fair amount of corrosion on the contacts. Pulling the harness to replace the connectors, remove the reserve lighting and turn signal regulator circuits. Replacing the old fuse box too. I'll take apart the hand controls and clean up the internals.

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Rejetting carbs after major work 31 Aug 2021 22:02 #854673

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I have rebuilt the harness, and now show 12.4V at the coils, just under the 12.6v I had at the battery. Rejjetted the carbs back to stock- 37.5 pilot, 120 main, needle on 3rd notch. Ran cleaner through them again just to be sure. Not much change, maybe a bit better. I went ahead and ordered 32.5 pilots and a set of mains 100 through 110. Plugs are sooty and piston looks wet even. Photos for reference. The cat didn't help much either. Terrible shop hand.

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Rejetting carbs after major work 02 Sep 2021 18:50 #854756

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Some times cheap pods will block the carb orifices. have you checked to see if they are obstructing the ports? have you tried running it without the filters?

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Last edit: by DoctoRot.

Rejetting carbs after major work 02 Sep 2021 19:08 #854757

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Plugs are carbon fouled. Usually a rich condition. As DoctoRot suggests check the pod fit and make sure none of the air port are blocked. You could be fighting a carbon fouled cylinder, piston, valves, etc.etc. Get new plugs. Don’t install them. Start the bike and let it warm up. Shut it off, swap in the new plugs and take the bike for a ride and give it a good ol’ Italian tune up. 
1976 KZ 900 A4 kzrider.com/forum/11-projects/613548-1976-kz-900-a4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.

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Last edit: by Mikaw.

Rejetting carbs after major work 02 Sep 2021 19:48 #854758

  • krazee1
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Former M.E. at Kawasaki Motors Manufacturing, Lincoln, NE
1966 W1 (the Z1 of 1966-50H.P. and 100mph!)
1974 Z1
1978 KZ1000 LTD
1976 KZ900B pile O parts
1980 KZ750E
1980 Honda XL250S (I know, wrong flavor!)

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Last edit: by krazee1.
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