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1978 KZ650 High RPM
- DaveKZR
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- TeK9iNe
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Try opening the fuel cap to see if that resolves the problem, as the breather could be clogged.
With engine hot (when its starts this issue), spray WD40 around the carb holders and elswhere along the intake. You will hear a sudden change in rpm/smoke out the exhaust if wd40 gets sucked in.
Make sure that the advancer unit behind the ignition plate rotates and returns properly, as this requires lubrication as per regular maintenence.
GL!
Motorcycle Shop Owner/Operator
79 Kawie Z1000 LTD
81 Kawie Z1000 CSR
83 Honda VT750C A
85 Kawie GPZ900 A2
86 Zukie GS1150 EG
93 Yamie XV1100 E
Lucky to have rolled many old bikes through my doors
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- MFolks
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1.Spray around the rubber ducting(boots) from the air filter box to the carbs with brake cleaner or WD-40.
2.Using an unlit propane torch with the gas turned on, do the same checking around the carb rubber bits.
If the idle rpm goes up, you've found your leak(s), also check at the carb holders(sometimes called manifolds) between the engine and carbs. They will crack from heat and age and require replacement. Replace the rubber snyc. plugs too if they are cracked.
Check to see if the mechanical ignition advancer is working, it's behind a CD sized cover on the right side of the engine. Give it a twist with the engine off and see if it returns to where it was.
If sticking,remove,clean,and reinstall.
Light lubrication with 3-in-one or sewing machine oil is about all it needs now and then.
1982 GPZ1100 B2
General Dynamics/Convair 1983-1993
GLCM BGM-109 Tomahawk, AGM-129A Advanced Cruise Missile (ACM)
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- Patton
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Would first inspect fitting of cables at carb belcrank.
Could try disconnecting cables at carb end, and see whether carb slides fully close without possible interference from the cables.
Good Fortune!
1973 Z1
KZ900 LTD
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- Patton
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Good Fortune!
1973 Z1
KZ900 LTD
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- DaveKZR
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Is this under the same cover as the cam tension shaft? What does the acutal ignition advancer look like and do you just spin it by hand?
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- BSKZ650
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to me your issue sounds more like a vaccumm leak or a throttle cable binding up.
you can remove the tank and work the throttle and watch to see if they are returning to the idle stop
77 kz650, owned for over 25 years
77 ltd1000, current rider
76 kz900, just waiting
73 z1,, gonna restore this one
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- DaveKZR
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- Patton
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...looked at the decel cable I saw a slight bit of slack at the carb end. In my mind I thought if I tighten it up it should pull the rpm back down....
Carb spring is supposed to return carb to fully closed idle position without needing any help from the decel cable.
Carb should function perfectly without any decel cable whatever.
Good Fortune!
1973 Z1
KZ900 LTD
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- DaveKZR
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So I adjusted the deccel cable back to the way it was before, and found an air box boot that had come half way off of the carb intake. I thought I was golden and looked forward to the ride home. Hopped on the bike in the afternoon and the first 4 gears accelerated fine, though they seemed rather short. This is my first bike and I've only had it a week so I'm not super sure, but they seem short. Anyway in fifth gear there is not really any acceleration past 65-70mph. Halfway through my commute home it starts acting up even more! I can't even be in fifth unless I hold the throttle in just the right spot. It is a tiny sweet spot, if I'm there it will accelerate to about 65 that's it. If I'm not in the sweet spot it sputters backfires, jerks and lurches. Very unpleasant. I shift down to 4th and the same only the sweet spot is slightly larger, shift to 3rd with rpm screaming and it accelerates nicely. The rpm also seem to be riding somewhat high as well. Sometimes when I was in fifth it would bog down all the way to about 20mph and backfire LOUDLY. Shift it to 4th, same thing. Really a nightmare of a ride home. Part way home I remembered someone mentioning opening the gas cap. Did this and it somewhat improved. It was a little smoother and not as much popping, but still wouldn't go above 70. Another thing I noticed, going uphill it just about died, not that large of hills either. But then going downhill she would open up to about 80. Also I looked one time when the rmm was high in idle and the bell crank was in the idle position, so that sounds like maybe a vacuum leak but I cannot get the idle to rise using lubrication spray. I have not looked into the ignition advance yet, that is tomorrow. Sorry to be so long winded! I appreciate all of the knowledge you guys provide on these forums, hopefully one day Ill be on the answering side of these threads.
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- TeK9iNe
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Carburetor tuning depends on the type of carb. I think you have regular slide carbs/non-CV, therefore:
The mixture/air screws are for tuning the idle, and have a small effect on the transtition to about 1/8th throttle.
The Pilot jets are drawn thru @ idle, and effect cruise up to just after 1/8th throttle as well.
The needle is responsible for all of the accelleration, right up to about 2/3 throttle, then continues to overlaps the main till about 7/8ths throttle.
The mains are from a small amount at 2/3rds throttle to WiedOpenThrottle.
If the idle screws are set close, then the idle shouldnt have any popping in the exhaust, and when revving, should return quickly to idle. If not, there is likely still an air leak, or sticking advancer.
As for your situation with the no power @ higher speeds, it sounds like your needles/or mains are too rich, but it depends on how much throttle input your using.
GL!
Motorcycle Shop Owner/Operator
79 Kawie Z1000 LTD
81 Kawie Z1000 CSR
83 Honda VT750C A
85 Kawie GPZ900 A2
86 Zukie GS1150 EG
93 Yamie XV1100 E
Lucky to have rolled many old bikes through my doors
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- Patton
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Performed compression test?
Ignition timing to specs?
Air filter clogged or obstructed?
Good Fortune!
1973 Z1
KZ900 LTD
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