Author Topic: Kawasaki GPZ 750  (Read 1257 times)

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Offline Bodain

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Kawasaki GPZ 750
« on: November 09, 2019, 12:49:42 PM »
Now that I'm retired... Chasing old bikes doesn't stop. About 4 months ago, I picked up 1984 Kawasaki GPZ 750. Hack hack bang bang and it's running. I originally tried to use original air box. Those rubbers were rock hard as one would expect so I trashed stock air box. These are CV carbs. So when it was first running on the center stand it would ran and rev great.. Then I took first ride.. Twist the trottle and no power. No big deal. I'll drill out the main jets. Done it tons of times on other bikes and it works great. Did a number of CB 750's with pod air filters like this. So I drill the main jets and got it to run fine. So it's a great little quick ride up to about 1/4 throttle.. Turn throttle wide open and it's like someone turned off the ignition. There is NOTHING. Not a flat spot that I can get past. There is just nothing... Fiddled with it for 2 months...but it wasn't a priority. The bike is a beast with just 1/4 throttle. So I drilled jets more. No change. I fiddled with restricting air flow into the pod air filters. Nothing seems to let this thing run at full throttle. There are 4 slots to adjust needle jet. I've been on the top and bottom slots. No change... Actually I'm perfectly fine with just 1/4 throttle cause it will spin up to 90 or so in a blink of an eye. It's actually becoming a matter of pride that I can't seem to make this thing run at full throttle.   I'm sure someone here has done similar battle with CV carbs.
2009 Suzuki TU250
2014 Honda Grom
1984 Kawasaki GPZ 750
2005 Yamaha Zuma 50
1974 Honda CB 750
1979 Kawasaki Z750 Twin

Offline MRieck

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Re: Kawasaki GPZ 750
« Reply #1 on: November 11, 2019, 06:42:33 AM »
The carb slide diaphragms may be damaged secondary to age.....the slides may not be fully opening (especially since needle height did not change anything.)
Owner of the "Million Dollar CB"

Offline Bodain

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Re: Kawasaki GPZ 750
« Reply #2 on: November 11, 2019, 06:24:27 PM »
Thanks for the thought. Certainly if the diaphrams were damaged the slides would not be able to open for lack of vacuum. I've had these carbs apart many time and the diaphrams appear fine. Yet it's almost like the main jet never comes in at full throttle. I've been messing with altering the air flow via the pods by blocking part of the pods with electrical tape. Yesterday it was warm here in Fort Worth and I took it out after further restricting air flow. Same problem exists. Generally if I suspect a problem somewhere in the carbs.. I want to reproduce the problem off the bike while the carbs are sitting on my bench. Hmmmmm... I think tomorrow I'm going to remove those carbs and get them on the bench. I'm going to attach a vacuum cleaner hose to the intake side of the carb and observe the action of slides.
2009 Suzuki TU250
2014 Honda Grom
1984 Kawasaki GPZ 750
2005 Yamaha Zuma 50
1974 Honda CB 750
1979 Kawasaki Z750 Twin