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.
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.
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.