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crazy idle
- newhouse
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- bountyhunter
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1979 KZ-750 Twin
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- Makarth
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I wonder if you may have a tear in the diaphragm (rubber suspension) around the carburetor piston?
i thought 78 still had manual slide carbs.
i would check the air screws on the carbs, someone may have tried to sync the carbs and back out the air screws too far out.
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- newhouse
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- Makarth
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- Z1109R Fin
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Synchronizing carbs means that you adjust the amount of vacuum in all carbs to same level (to which level is pretty much insignificant). This is done by adjusting THROTTLE BODY BUTTERFLY VALVES and nothing else.
Click: www.carbtune.co.uk/carboprn.html
I really mean no offence by writing so pluntly here but this is a pretty common misunderstanding and even today I´ve read this same misleading advise about synching twice.
Z1000R ´83...Slightly modified...
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- Z1109R Fin
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Air/pilot screw has nothing to do with carb synchronizing!
Synchronizing carbs means that you adjust the amount of vacuum in all carbs to same level (to which level is pretty much insignificant). This is done by adjusting THROTTLE BODY BUTTERFLY VALVES and nothing else.
Click: www.carbtune.co.uk/carboprn.html
I really mean no offence by writing so pluntly here but this is a pretty common misunderstanding and even today I´ve read this same misleading advise about synching twice.
Air/fuel -screw is used to adjust the mixture from idle up to 1/4 throttle.
Idle screw is used to adjust the level of idle and has nothing to do with mixture. It´s just a manual thingy to adjust how far down the throttle linkage can go.
Sorry:blush: I meant to edit not quote my post...
Z1000R ´83...Slightly modified...
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- mtkawboy
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78-KZ1000/1105, 80 KZ1000, 82 Kawasaki GPZ750, 95 Harley Fatboy, 80 Suzuki GS1100ET, 81 GS1100E parts bike, 83 GS1100SD Katana/1394,78 Yamaha XT500, 81 Yamaha XS650, 78 Yamaha XS650E, 48 Whizzer model J motorbike, 71 Honda CT70H, 71 Honda CT70, 81 IT 250 Yamaha,82 Honda XL100S owned
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- wiredgeorge
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Uh oh... we are going to disagree here. If the air fuel mixture is way off, the bike will run so poorly that the carb sync is impossible. I suggest that the idle air/fuel mixture be adjusted prior to synchronizing.
There is no real way to know how to answer this problem due to the lack of info provided... Does the idle HANG and take a while to come back down or is it erratic... shoot up high when you are idling on a random basis?
And folks, there are no throttle butterfly valves or slide diaphragms on these carburetors. The reason that the idle adjust screw isn't touching the stop and the bike idles too high is that a proper bench sync was not done. The bench sync puts the slides in the middle of the adjustment range of the screw... in other words the slides will open and close where they should.
mtkawboy mentioned throttle cable... that is always a possibility with idle issues. If the cables is mis-routed or binding, the idle will be messed up. If the throttle is riding on a bed of old rust up under the right switch gear, binding will occur as well. Taking off your throttle sleeve every now and again and cleaning and geasing the bar end makes a lot of sense.
wiredgeorge Motorcycle Carburetors
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Too many bikes to list!
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- Z1109R Fin
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Z1109R Fin wrote, "Air/pilot screw has nothing to do with carb synchronizing!"
Uh oh... we are going to disagree here. If the air fuel mixture is way off, the bike will run so poorly that the carb sync is impossible. I suggest that the idle air/fuel mixture be adjusted prior to synchronizing.
There is no real way to know how to answer this problem due to the lack of info provided... Does the idle HANG and take a while to come back down or is it erratic... shoot up high when you are idling on a random basis?
And folks, there are no throttle butterfly valves or slide diaphragms on these carburetors. The reason that the idle adjust screw isn't touching the stop and the bike idles too high is that a proper bench sync was not done. The bench sync puts the slides in the middle of the adjustment range of the screw... in other words the slides will open and close where they should.
mtkawboy mentioned throttle cable... that is always a possibility with idle issues. If the cables is mis-routed or binding, the idle will be messed up. If the throttle is riding on a bed of old rust up under the right switch gear, binding will occur as well. Taking off your throttle sleeve every now and again and cleaning and geasing the bar end makes a lot of sense.
WG, I´m no way trying to be a wiseguy or a guru here but...Sychronizing as a term means balancing the vacuum that either butterfly valves or manual slides create inside the carb venturi. Vacuum must be even in order to suck even amount of fuel in to all cylinders. This is why I wanted to make clear what syching means. All other adjustements like air/fuel, needle position, jetting are related to mixture adjustement.
Of course carbs should be on the bal park before you can start adjusting them in any ways. Therefore bench-sync is #1 in work order, then basic jetting to get the bike running and then you should sych them and stert finding best jetting.
My experience in carbs is some what limited. I got (bike is ´83 ELR) my BS34´s running pretty nice after 998->1109cc bore, mild porting, K&N pods, 4-1 open exhaust and so on. Then I bought TM33 flat-slides (off a GSXR), dyna coils and some other bits and pieces and again got them running pretty well. Actually last winter bought a A/F Ratio meter (bolted on all the time) ang Morgans CarbTune. These two gadgets made a world of difference compared to test-ride-bummer-test-ride-oh-crap -method. This summer it really pulls like a maniac.
I´ve been reading post on KZR for a few years now and would like to see some kind of a basic walk-through to settin up carbs. Now people are asking the same question over and over again which means that those (not me) who really know about these things get really tired to writing here all the time.
Please understand that again this is no offence, KZR and some other forums have been a tremendous help for me.
Z1000R ´83...Slightly modified...
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- wiredgeorge
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I have synchronized THOUSANDS of sets of carburetors and made a statement based on that experience and will stand by it. Making the idle mixture right prior to synchronizing any carburetor is necessary and the closer to correct, the easier it is to sync. I also have an EGA and several very professional sets of sync gauges. They DO NOT make all the difference in the world when tuning; experience does.
wiredgeorge Motorcycle Carburetors
Mico TX
www.wgcarbs.com
Too many bikes to list!
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- KZErider
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"Repetition strengthens and confirms".
P.S. I'm "computer illiterate",too, but I'm still learning.
81 KZ750E2(project), 81 KZ750E2(parts donor), 87 BMW K 75C - got it runnin, didn't care for it, holding for family member, 79 CB650(project) Nomad 1700, VStar 950
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