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Re-Visiting the Runs like sh*t 81 GPz550

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09 Sep 2024 07:19 #904127 by chopper1963
Re-Visiting the Runs like sh*t 81 GPz550 was created by chopper1963
The beater 1981 GPz550--STOCK--still will not come around.
Carbs are clean.
Good spark on all plugs.
Good compression
The advance/pick up is working
The timing is spot on.

Still runs like crap on the center two cylinders.

It's frustrating as all hell. The carbs are clean! There is good spark! There is good compression!

 

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  • Wookie58
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09 Sep 2024 07:42 #904129 by Wookie58
Replied by Wookie58 on topic Re-Visiting the Runs like sh*t 81 GPz550
Have you checked "valve clearance" (big gaps will mean the valves open less ?)
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09 Sep 2024 10:32 #904136 by chopper1963
Replied by chopper1963 on topic Re-Visiting the Runs like sh*t 81 GPz550
Not in a while but I guess I can.

The good compression all the way across leads me to believe that the valve clearance is good. Is that a bad thing?

 

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09 Sep 2024 10:33 - 09 Sep 2024 10:35 #904137 by Wookie58
Replied by Wookie58 on topic Re-Visiting the Runs like sh*t 81 GPz550

Not in a while but I guess I can.

The good compression all the way across leads me to believe that the valve clearance is good. Is that a bad thing?



 
Tight valves will effect compression, loose ones "not so much"
Is it possible to see into the carbs when the motor is running, if so are all four slides lifting equally ?
Last edit: 09 Sep 2024 10:35 by Wookie58.
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09 Sep 2024 16:53 #904154 by Nessism
Replied by Nessism on topic Re-Visiting the Runs like sh*t 81 GPz550
With good compression, clean carbs, and strong spark, I don't know what's left?  Could the center two exhaust pipes be plugged up?  And when you say clean carbs, did you ungang them and soak the bodies in carb dip after removing all the various parts?  Shoot carb spray through the pilot passages, and make sure it comes out the proper location on each carb?

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  • SWest
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09 Sep 2024 21:28 #904162 by SWest
Replied by SWest on topic Re-Visiting the Runs like sh*t 81 GPz550
I'd take a good look at the plugs, wires and coil. Have you used a timing light on them? You can look for a miss that way.
Steve
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10 Sep 2024 03:29 #904167 by asphalt900
Replied by asphalt900 on topic Re-Visiting the Runs like sh*t 81 GPz550
Going to take a wild guess here but i have ran across a couple Kawasaki 4cyl KZ750's that also had seemingly decent enough to start compression. Only to find out later that the head had warped, lifting 2 and 3 off their head gasket. But that's just a wild scenario i know. Being it's confined to 2/3 issues try swapping coil leads around and see if problem goes to 1/4. Have also experienced issues with the IC IGNITER and pick-ups on your era of Kawasaki. While it seemed to have decent enough spark still didn't function correctly. Switched out to a Dyna S and problem mysteriously disappeared, ha.   

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  • ThatGPzGuy
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10 Sep 2024 05:23 #904172 by ThatGPzGuy
Replied by ThatGPzGuy on topic Re-Visiting the Runs like sh*t 81 GPz550
If it's cylinders 2 & 3 that points to the one thing they have in common: the coil. @Asphalt900 has good advice there. Otherwise, I would suspect the pilots are not clean on those carbs. 
Question: How do you know the center two cylinders are not running well? 

Jim
North GA
2016 Yamaha FJR1300ES
1982 GPz750 R1
1974 Kawasaki H1
1976 Kawasaki KZ400
1979 Yamaha XS650 cafe'
2001 KZ1000P
2001 Yamaha YZ426
1981 Honda XR200 stroked in an '89 CR125 chassis
1965 Mustang
1967 Triumph GT6
1976 Bronco
"If you didn't build it, it's not really yours"

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10 Sep 2024 17:44 #904202 by chopper1963
Replied by chopper1963 on topic Re-Visiting the Runs like sh*t 81 GPz550
<<<The timing is spot on.>>>

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10 Sep 2024 18:37 #904204 by Nerdy
Replied by Nerdy on topic Re-Visiting the Runs like sh*t 81 GPz550

 
Question: How do you know the center two cylinders are not running well? 
 

That is a good question. An infrared thermometer (~$15 from Harbor Freight) will show the temp variances in the headers - a useful piece of info.

1979 KZ400 Gifted to a couple of nephews
1967 Yamaha YCS1 Bonanza
1980 KZ440B
1981 Yamaha XT250H
1981 KZ440 LTD project bike
1981 GPz550
2013 Yamaha FZ6R
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13 Sep 2024 08:54 #904266 by chopper1963
Replied by chopper1963 on topic Re-Visiting the Runs like sh*t 81 GPz550
Bike runs on four top and mid range. But won't run on center two at all at idle. So frustrating

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13 Sep 2024 09:23 - 13 Sep 2024 09:25 #904268 by TexasKZ
Replied by TexasKZ on topic Re-Visiting the Runs like sh*t 81 GPz550

Bike runs on four top and mid range. But won't run on center two at all at idle. So frustrating
Makes me suspect pilot circuits, either clogged or damaged. Perhaps mixture screws with broken tips, pilot jets wallowed out or pilot passageways gouged out by too-rough cleaning?
If the low speed mixture is way off, either lean or rich, those cylinders will not fire until the rpm is high enough to transition to the main circuit.

As asked above, how are you sure the middle two are the ones not firing at idle?

1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

www.kzrider.com/11-projects/620336-anoth...uild-thread?start=24
Last edit: 13 Sep 2024 09:25 by TexasKZ.
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