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Kawasaki KZ 750 LTD; Engine racing
Topic Started: Nov 4 2017, 01:00 PM (1,065 Views)
geofflucas
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Hi all. I have a 1983 Kawasaki KZ 750 ( us import ) that I have been renovating for a couple of years now, on and off. The bike is almost ready to MOT and register with the DVLA. The bike is a little hard to start, but eventually starts with a little squirt of Easy Start into the air box. After ticking over for a while the engine suddenly races up to 4000 RPM and stays there until I kill the motor. The carbs have been stripped and each part ultrasonically cleaned several times. New gaskets and a carb refurb kit has been fitted to each Keihin CV34 carbs. All the air box to carb rubbers are new, supple without any cracks. As it is a US model, it is fitted with the Air suction system from the air box to the top of the OCH covers to reed valves. The tickover is fully backed off so the increase in rev's are not attributed to this. There is fresh fuel in the tank. The throttle cable has free movement in the sleeve. I am at a loss what to do next to cure he high rev's after the engine warms up. Any advice or ideas would be appreciated.
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ChrisGPZ600R
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100 MPH
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I would check the carb adjustment, hanging revs is usually lean/rich mixture.
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geofflucas
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Hi. Thanks for your reply. I have checked the carb settings and are all set as the manual states.
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ChrisGPZ600R
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100 MPH
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Check possible vacuum leak.

All carbs balanced properly?

Also, the firing order correct? Usually it is 1,2,4,3.

To find the culprit cylinder, plug one HT lead out one at a time and start engine when warm. See if still hangs after blipping throttle. (it will run rough, but can tell you the offending cylinder/s)
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geofflucas
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Thanks Chris. That will give me something to look at when i get time.
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hugojose
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Humble Motorcyclist
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I hate pollution of course, but you could also eliminate the "Air Suction" US required system to simplify things, as this is operated by vacuum and another potential source of leaks. If you do remove it, all you have to do is plug the air box, cap the carbs nipples, and interconnect the reed valve takes with a hose in between. Am in the US and did this to eliminate clutter many years ago. Other than using engine vacuum, the system (or its removal) does not affect engine performance in any way, as it simply routes fresh air into the exhaust.

If boots between carbs and engine are sealing, then the other remaining source of engine vacuum leak would be the fuel petcock, if it is vacuum operated.
Edited by hugojose, May 27 2018, 10:14 PM.
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geofflucas
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Thanks for the information. NOS vacuum operated fuel petcock fitted.
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