Z1100st poor running - Kawasaki Motorcycle Forums
 
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post #1 of 7 (permalink) Old 06-01-2019, 03:36 PM Thread Starter
Muddiford
 
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Z1100st poor running

Hi all. I have a 1981 1100a which used to run ok but is now running rough, struggles to tick over and revs flat out when you blip the throttle. I rebuilt the carbs with new jets and float needles. The fuel level is correct on all four and they are reasonable well balanced. New carb rubber throats and air filter. Timing is correct, checked with timing light, new fuel in tank. New plugs and I've just spent a tidy sum in converting it back to original spec as it had the wrong headlight and lamp mounts. I've got to the point of viewing the sledgehammer with increasing affection and the bike is fast running out of time before I break it and sell the bits. It passed mot with no advisories last month but is now impossible to ride. If anyone has an idea of what direction to go, I'll be eternally grateful. I've been in the motor trade for 45 years and this bike is making me feel like a hopeless novice!! Sarcasm and leg pulling more than welcome if attached to some help! Thank you in advance.
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post #2 of 7 (permalink) Old 06-01-2019, 05:32 PM
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First thing I'd do is charge the battery with a good motorcycle smart charger & do a load test >> even if new. never assume a battery is good. The motorcycle needs a good, fully charged battery to start & run right.

Another problem could be the spark plug wire connections as they become poor from oxidation over time >> I would redo all of the connections. Unscrew the ribbed compression boots at the coils; the plug caps unscrew from the spark plug wires. I would nip off the ends a tad. Or go ahead & get new spark plug wires. You can reuse the o-rings n stuff on the old plug wires where they connect at the stock coils. you can also reuse the stock sheathing.

If the ignition coils are the originals, you may need to replace them. Sometimes they test fine cold, but when they get hot, they fail from internal shorts or something. A simple test is to ride the bike to warm up the engine, preferable doing a high speed run, then stop & feel the coils >> they should be warm, not hot >> press hard with your fingers. Mine were very hot to the touch, so I got green Dyna 3 ohm coils. The grey Dyna 2.2 ohm are probably a better match for the ignition system. There are also Accel coils & some guys install the ignition coil from a Buck Grand National 6-cylinder then adapt the wires (credit to ELR658).

Also, be sure to clean, check & lubricate the timing advancer. Separate the rotor from the advancer body to lubricate it & fill the groove with grease (if yours has the groove). After reassembly, check that the springs are good, not stretched or deformed or anything, then operate the rotor >> it should snap back. I think I used high temp wheel bearing grease the last time I serviced my timing advancer.
....

1981 KZ650-CSR. Competition, Sports & Road.
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post #3 of 7 (permalink) Old 06-02-2019, 05:35 AM
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..sure it does not have a vacuum leak??????
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post #4 of 7 (permalink) Old 06-02-2019, 09:07 AM
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I like that answer much better plus it's a lot shorter. hee. My petcock diaphragm was bad one time & the bike ran like crap as the #2 cylinder became out of whack.






...

1981 KZ650-CSR. Competition, Sports & Road.
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post #5 of 7 (permalink) Old 06-05-2019, 10:28 PM
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Sounds to me like it is pulling unmetered air. Carb holders are suspect if they haven't ever been replaced. Essentially that is what Hugojose is pointing too (I'm not trying to speak for you Hugo but that is how I read it). A vacuum leak or leak at the carb holders will cause exactly what you are talking about. Hard starts from too much air for the fuel and once you finally get it lit the air leak acts like an open throttle which pulls more fuel and the engine spools up.

Having said that I agree with everything Martin said as being important things to do to get a proper running vintage motorcycle and improved starting.

AJ aka AJsfirehawk

83 KZ1100 LTD
80 KZ1000 Z1 Classic
79 KZ650 D2
06 ZG1000 Concours
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post #6 of 7 (permalink) Old 06-07-2019, 08:47 AM
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First thing to check is the throttle cable. Not sure what carbs are on this bike but if the cable has no slack, the throttle will race. There should be about 1/8" deflection down at the assembly cable holding bracket when you take your finger and push the throttle cable sideways. What type carburetors are being discussed?

wiredgeorge
Texas Hill Country
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post #7 of 7 (permalink) Old 06-10-2019, 04:45 PM
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I'm not sure exactly how it is running as your description was a bit puzzling to me.
Are you saying the throttle hangs or races when you let off of the gas?
My old gpz had a hanging throttle and it turned out to be plugged pilot jets. It also did not run that well at part throttle but the hanging throttle was the most annoying.

1986 LTD 454
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