Z1 900 bogging down at mid rpm range 4k to 5k

I have the bike timed just right, and have done all the necessary stuff to get it running right. The plugs are still sooty (did the coil rewire already). I was told by a bike shop here in NC (he works on old KZ's) that since the plugs are sooty, I am getting to much fuel and I need to lean up my needles by moving the clip up one notch at a time on them until it is running right. Does this make any sense to you guys? I dont want to tear into it for nothing. Thanks, Joe.

Ok, I decided to go ahead and move the clips up one notch on the needles. I noticed that the #3 carbs clip was set on the very bottom notch, and the rest were on the second from bottom. #3 looked a little scarred up from the PO on the inside of round piece. The needle itself looked a little scarred up at the second slot. Right now I have all four set at the third from the bottom, and it sounds like it is starving for fuel, basically what it was doing at higher rpms when you twisted the throttle pretty good. Am I wasting my time? Should I set them all on the very bottom notch or on the second from bottom?

jdsmithinc wrote:

...I have the bike timed just right, and have done all the necessary stuff to get it running right. The plugs are still sooty (did the coil rewire already). I was told by a bike shop here in NC (he works on old KZ's) that since the plugs are sooty, I am getting to much fuel and I need to lean up my needles by moving the clip up one notch at a time on them until it is running right. Does this make any sense to you guys? I dont want to tear into it for nothing...

Ok, I decided to go ahead and move the clips up one notch on the needles. I noticed that the #3 carbs clip was set on the very bottom notch, and the rest were on the second from bottom. #3 looked a little scarred up from the PO on the inside of round piece. The needle itself looked a little scarred up at the second slot. Right now I have all four set at the third from the bottom, and it sounds like it is starving for fuel, basically what it was doing at higher rpms when you twisted the throttle pretty good. Am I wasting my time? Should I set them all on the very bottom notch or on the second from bottom?

I dont want to tear into it for nothing -- a legitimate concern here, because even perfect carbs cannot compensate for faults in non-carb components.

This information from wiredgeorge's website says it best -- Click here > wg's site

I have the bike timed just right -- that's good, and would hope that a strobe-type timing light was used to also assure proper operation of the advancer by watching it move back and forth while changing the rpm.

did the coil rewire already -- that's good, and should assure battery voltage is getting to the coil. But is battery voltage adequate (12-13 volts at idle, and 14-16 volts at 3000-4000 rpm, measured across the battery terminals)? But remember, adequate voltage to coil does not assure good quality spark at the plug. What is spark quality at tip of plug -- good fat spark?

Has compression been tested?
Are valve clearances within specs?
Cam chain slack properly adjusted?
Clean and clear air filter (and not blocked by something like a shop rag stored underneath the seat)?

Correct carb float bowl fuel levels verified by the clear plastic tube test?

Usually best to not fool with any carb adjustments or alterations until all the above non-carb components and floatbowl fuel levels are up to snuff.

Then and only then might be some need to address the carbs. Usually the oem needle clip position is correct. It doesn't mysteriously morph into an overly rich position. The clip positions in the present case were obviously incorrect. They should all be the same. And set at oem specs, which I believe is the middle position. Would consider changing the clip position to something different from oem specs as an act of final desperation after knowing without doubt that all other carb internals are perfect, including proper size main jet, fuel level, etc.

Right now I have all four set at the third from the bottom -- if that's the middle clip position and per oem factory specs, would leave them in that middle clip position.

all four set at the third from the bottom, and it sounds like it is starving for fuel, basically what it was doing at higher rpms when you twisted the throttle pretty good -- are plugs still sooty?

Am I wasting my time? Should I set them all on the very bottom notch or on the second from bottom? -- Moving all the jet needle clips back to the factory specified middle position was not a waste of time. Any further carb fiddling before attending to the above mentioned non-carb components is a waste of time.

Am thinking there's nothing here that won't be found in the FSM.

Hoping to be of help, and don't mean to sound preachy.

Good Luck!

1. Advancer is working properly
2. Voltage is fine.
3. No way to test compression
4. Dont even want to think about tearing the head off for valves
5. Cam chain slack? How do you adjust this?
6. Filters are brand new.
7. Built a stand for the carbs to set the float levels
8. Plugs still sooty.
9. I think I am just going to sell it, and get one that runs. I think I am in over my head.
10. If there is anyone in my area that may be able to come over and help me out I am all in!! I can pay!

jdsmithinc wrote:

1. Advancer is working properly
2. Voltage is fine.
3. No way to test compression
4. Dont even want to think about tearing the head off for valves
5. Cam chain slack? How do you adjust this?
6. Filters are brand new.
7. Built a stand for the carbs to set the float levels
8. Plugs still sooty.
9. I think I am just going to sell it, and get one that runs. I think I am in over my head.
10. If there is anyone in my area that may be able to come over and help me out I am all in!! I can pay!

Thanks for the good report.

Checking valve clearances is a routine maintenance item, which does require removal and replacement of the valve cover (not difficult), but does not require tearing the head off. Feeler gauges in the necessary smaller sizes are required.

No way to test compression -- A compression tester is relatively inexpensive, and often available on loan from local auto-supply store such as AutoZone.

Cam chain slack? How do you adjust this? -- This routine maintenance item is quickly and easily performed, and doesn't require removing anything (except possibly the points cover to set crank position at the T mark (TDC) during the adjustment).

in over my head -- anyone unfamiliar with these bikes is similarly situated without an FSM (factory service manual) or good aftermarket manual at hand. Although an on-site search often provides detailed procedures.

If there is anyone in my area that may be able to come over and help me out I am all in!! I can pay -- Getting some local help from a more experienced owner is a good idea. But would pay for an FSM. These often appear on eBay. It's an essential tool.

going to sell it, and get one that runs -- okay, but won't prevent need for attending to routine maintenance (same as when they were brand-new).

Good Luck!