Hey everybody. I’ve got a 1980 kz1000G that I picked up that was in pretty good condition and couldn’t pass up. I’ve been working on this bike all summer and fall long and I’m very close to getting it perfect. It’s got a set of vm26 carbs off a 77 kz1000 with the 5CN8 needle. Over the summer I took on a head job since the bike needed a new head gasket anyways, cleaned all the valves, replaced springs and seals, and cut the seats myself. I’ve got good compression and no leak on all cylinders and the bike ran pretty decent with pod filters on. I upgraded coils and made sure I was getting the proper resistance on the spark circuit and got a nice fat blue spark from the spark plugs. Another task I took on was fitting a center stand to the bike so I could do chain maintenance and such. This led to me cutting up my 4 into 1 exhaust and fabbing up my own. Once I got the bike running it felt much better than before doing the head job but as you all know, pod filters suck to tune, especially on the vm26 carbs and leave a lot to be desired on the low end and mid range. So I just purchased a repro z1 airbox with a k&n filter in it to throw on the bike. I just put it on and took it for a ride and the bike died when I was at WOT cause I’m pretty sure it was running way too rich with the pod filter jetting in it. It currently has 20 size pilot jets and 115 size main jets with the needle clipped on the fourth slot. I’m about to purchase some new jets now and wanted to hear what you guys thought. I’m thinking of going back to 17.5 size pilots with 110 or 112.5 size mains and the needle back on the third slot. Let me know if you guys have any suggestions or advice for this. Thanks in advance!!
hardrockminer wrote: I think thats a good position to start. Original configuration was 17.5 pilot, 107.5 main and 5CN8 needle in the middle position. Look up zed1only and consider purchasing a set of his restrictor jets.
Those jets sound like a good starting point. With a stock airbox they might be perfect.
Many of the early VM26 carbs came with 15 pilots and 105 mains. 17.5/107.5 seems right. Maybe also get some larger mains while you are ordering.
Wow. Thank you guys for the help. Especially the thread about the air corrector jets and such. I somehow managed to overlook that thread when I was reading up on these carbs. I’ll have to get some of those in case I decide to go back to pods if I get annoyed with the airbox lol. I’m gonna get a pair of 107.5 and 110 mains and see if the 110s run good since I have one of the k&n filters in and my exhaust has no baffle in it at all. Thanks everybody for the help. I haven’t seen a lot of threads about the z1 classic. I’m assuming it’s a little rare since it was only made for one year haha. Thanks again guys!
So I’ve got some updates to this thread. Bike still does not run right and it’s driving me nuts haha. I fitted the z1 airbox with the k&n air filter. Reclipped the needle into the third slot, changed out the pilot jets for 17.5, and the main jets for 110. Before this I had the vm26 carbs set for pod filters with 20 pilots, 115 mains, and the needle in the 4th slot. The bike ran pretty good at these settings with the airbox on other than stalling out and dying at wide open throttle. (I just wanted to see how it would run prior to changes). After readjusting the carbs with the fuel mixture screw set to 1-1/2 turns out. The bike was harder to start but idled okay. When I went to go ride it around, it died again (which I assumed was from a rich main jet). On the way home it felt and sounded like it was running on 3 cylinders. After getting it home I went to check the spark plugs to see what they looked like and they were a little wet. Now at this step I managed to pull the threads out of one of the spark plug holes. I used a thread chaser and put the spark plug back in but it was barely holding because when I went to tune it again, it shot the cyl 1 spark plug straight out of the head haha. After many days of repairing the spark plug hole with an insert and changing the mains to 107.5. I just went to start it and it idled smoother even though it took forever for it to finally start, however, if I even touch the throttle after the choke is off, it immediately dies. I’m at my wits end with this bike. It’s been months now and I am so over working on this thing haha. I have other projects to work on. Do you guys have any suggestions on what to do with this nightmare? Just FYI, I rechecked my timing and I didn’t jump a tooth and all my valve clearances are within spec.
First off, thank you so much for all the informative pages! I don’t have a manual but I’ve been scraping by finding what I need here on the forums. As far as maintenance, I replaced the spark plugs, wires, and coils and have tested them again to make sure they’re all functioning good. I also set float levels to spec and check them each time I have the carbs off. Valve lash and timing is also good. The ignition is electronic but I made sure my timing advancer was operating correctly. I also sprayed some starter fluid around the carb boots to make sure I wasn’t getting any vacuum leak and There wasn’t any change in rpm level when I did that. My only thought is to maybe change the needle position and pilot jet back to how I had them with the pods since it felt like it was idling smooth with strong midrange then, but keep the main jet at a 107.5 so I don’t foul the plugs out at wide open throttle. I’m so sick of taking these carbs on and off and setting everything up just to be disappointed again!
Well you have covered a lot. Have you vacuum synced the carbs or at least bench synced them. The jet needle has no effect on idle. Pilot circuit, synchronizeing and pilot fuel screws will affect idle. Have you run a compression test.
EDIT, I’m not familiar with your bike except that I know it was factory fuel injection. Have you made sure you have plugged or disabled all of the fuel injection items. Isn’t there injection ports in the head?
I did a compression test after I completed the head job to make sure it was holding compression. I guess it wouldn’t hurt to do another one, I don’t see how compression would’ve been lost between then and now but it never hurts to recheck. All injections ports have been sealed with plugs and sealant. The carbs were bench synced with a piece of 0.030” welding wire since it’s the closest to 0.7mm that I could find around the house. I checked to make sure they all looked equal last time I pulled the carbs off but I’ll check again just to be certain. This is why I’m stumped haha. I’ve gone over all these things religiously and made sure they were all to spec so I’m just lost. That’s why I feel it’s all in the carbs at this point. Since it was idling good with a size 20 pilot, maybe I’ll try those again. I’ve read on one forum post on here that a guy had to size up because the stock size pilot wasn’t reacting well to new gas. I live on the east coast in Virginia where ethanol is in all of our fuel so maybe that’s the cause? That’s my only thought at this point. It just goes against what my eyes are telling me when I check the spark plugs after idling the bike and they seem to be black. I was getting some pops out of the exhaust which is another indicator that hints towards a rich pilot mixture. Could just be my eyes deceiving me or some voodoo old motorcycle magic that is beyond my understanding in 25 years of life haha. I’m trying not to lose hope. One odd thing I did notice (not sure if this has any affect on my situation) was that when the bike was idling and I was attempting to adjust the pilot screw on cyl 4, there was the tiniest little arc between the screwdriver bit and the pilot screw. I’ve checked and rechecked the ground connection though and the engine is grounded to the battery ground.
The float level on those carbs is 3 mm plus or minus 0.5. What have you set them at? Do you have the original throttle valves with 1.5 mm cutaway?
If you think you are running too rich at idle you should be thinking about how extra fuel might be getting into the combustion chamber. One way is through worn choke plungers. Another is worn needles or needle jets. Another is incorrect float level.
I have a couple of Z1B's restored, an '80 KZ1000LTD restored, a 1981 KZ550 restored and a 2008 KLR 650 for off road fun. My wife has a 2019 Suzuki DR 650 for on and off road.