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I just had to do some fixes on my 1993 Kawasaki ZR750. I had some rust in the tank so I got it cleaned and sealed. To be thorough I also checked the rest of the system. Here's what I did:

  • Disassemble the carburetor, clean the housing in an ultrasonic bath, replace valves, needle, etc. and perform the basic setup by the books. After the bike was running again I synchronized them, which was barely necessary.
  • Cleaning the petcock in an ultrasonic bath
  • Performing an oil and filter change.
  • Removing the oil pan, cleaning the oil screen and sealing it again
  • To be able to remove the oil pan I had to remove the whole exhaust with manifolds
  • Replacing the spark plugs
  • I also installed a new chain kit

After I did this it first seemed to work like a charm. Then I got to a road with higher speed limit. The engine just cuts of power at about 6000 rpm in neutral. In the 5th gear this is about 95 km/h at 5500 rpm. This doesn't seem to be a gradual loss of power. Until that rpm value it runs better than before but then it just stops.
If I then pull the clutch and completely stay of the gas, the rpm stays at 6000 and doesn't drop (at least not in the first few seconds). I have to pull it down with the engine break.

What could be the issue here? I'm suspecting a problem with the carburetor setup. I already checked the throttle cables. Also the fuel flow from tank to carburetor seems to be fine.

EDIT

So I took her for another test drive today. It was like 10°C colder than last time. I needed full choke for a long time or she stalled in idle. I think it took about 15-20 minutes until idle rpm was reliable.
I can also confirm the behavior in neutral without load. I can spin her to 6000 rpm without any problems, then she cuts of and stays there until I engage a gear and apply some load.

Considering the cold behavior I guess DucatiKiller is right and she is running way too lean. But even if so I do not understand why the rpm doesn't drop and need some aid regarding the setup.

EDIT 2

Managed to do another test drive. First I adjusted the idle mixture a good bit richer and turned up the idling supply a little. Still needed choke for a few minutes but was running smoothly at 1500 rpm idle real quick.

Then I took care of the non dropping rpm. If I do it without load, it now stays at 6500-7000 rpm. If I give the damper flaps a little nudge directly at the lever, it comes down. So I think the throttle reset cable has a little too much clearance. Should be easy to fix.

The problem with the missing power is no problem with the throttle cable. But I got a little further as well. I noticed that this is not depended on rpm but on the amount of throttle. At high throttle she has no power. But when I release the throttle to a certain point, the power is back. It's not the full power but I managed to get her to a 115 now. Also I noticed a faint "rattling" in the no power zone. Like a cellphone vibrating on a table maybe, but continuous.
I'm guess now that the low load valve in the carburetor works fine and the high load valve doesn't open up for some reason.

  • With the bike sitting still, in neutral, does it idle well? If you twist the throttle what happens? When you let go of the throttle what happens? – JPhi1618 May 17 '16 at 21:20
  • @JPhi1618 Neutral is fine at 1100 rpm as it should be. I'm going to check the behavior in neutral in detail tomorrow afternoon. It's past 11 pm here and I think my neighbors wouldn't be too excited about it ;-) – André Stannek May 17 '16 at 21:36
  • If you are idling and in neutral, if you rev the engine, do the RPM's hang a bit at 6,000RPM's and then drop down considerably? If it does, what is the final idle RPM? Does it stall after the high revving? – DucatiKiller May 18 '16 at 1:29
  • @AndréStannek I think you might have some unmetered air and a severe lean condition. It depends on how you answer the questions above. – DucatiKiller May 18 '16 at 1:58
  • @AndréStannek I just saw your update. With the hanging idle at 6000 RPM, have you tried to adjust down your idle with your idle screw? Have you inspected your cable run for the throttle cable, is it kinked or binding up? is there a physical impedance of something that is preventing the complete closure of your butterfly? moab 's response below regarding some kind of physical issue with the throttle being unable to close all way through a wire harness being in the way or something of that sort.....it seems to make sense. – DucatiKiller May 18 '16 at 23:28
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If I then pull the clutch and completely stay of the gas, the rpm stays at 6000 and doesn't drop

Sounds like you did something wrong during the rebuild, all you can do is pull the carbs and check your work, also check throttle cables for proper routing and adjustment.

Did you clean the fuel tank valve and screen?

  • Thanks for your answer. I also cleaned the valve and already checked the throttle cables. I've edited my question regarding this. I was hoping for something more specific to look for since I, of course, triple checked if everything is in it's place during reassembly ;-) – André Stannek May 17 '16 at 20:27
  • 1
    Something is holding the throttle open. – Moab May 17 '16 at 21:08

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