z1classic with carbs

I have an 80' z1classic that has carbs now. Looking in the clymer book they look like the diagram for 77. they have air mixture screw no fuel mixture. the bike sat for ten years before i got it, I cleaned the carbs changed the oil etc... to see if it would run good before to much investment. It ran and drove fantastic so i took everything apart mostely for cleaning, put it back and now..
It runs great until you close the choke, or if I put it in gear and let the clutch out it boggs down and dies under
3000 rpm. does this sound like a carb problem or something else.

Funny, I had the exact same problem with my Z1 classic but it retains its stock fuel injection. Ultimately I found several dicey things I had to repair to get it proper.

If you have to keep it choked the round idle wheel may have gotten turned out too much -- this idle wheel is just behind that butterfly-looking throttle cable pulley:




Now, I have no idea what carbs they put on your Z1 but the picture above shows what this round thumbwheel *looks* like. It may not be in the exact same position as shown here, for example for all I know the carbs they put on your Z1 have the thumbscrew in the center and below the level of all the float bowls, but look for this and turn in inward until you hear your idle pick up.

If this thumbscrew is unscrewed too much you will have your symptoms.

Get back to us here if that has no effect, the next check will be 'what was your process when cleaning the carbs -- did you remove all the jets/use carb cleaner and compressed air' kind of questions for you.

And check the ignition advancer behind the right crankshaft engine cover -- if it sat 10 years see if the advancer moves freely and springs back into normal position easily and if not, lubricate it.

Thanks ill try that and post results, it also has pod filters and i want to bypass the emmission valves for the exhaust, how much does that affect the carbs

Yah, That's not my problem I guess I'll have to take the carbs apart again and check all the jet sizes and look in the forums for another thread that might tell me the sizes I need
I'm pretty sure I blew out all the passages and jets I'll do it again then I'm stumped. The clutch is good, valve clearance is good, has good compression, the only thing I'm not sure of is the carbs and the air valve and case breather

Z1class wrote:

Thanks ill try that and post results, it also has pod filters and i want to bypass the emmission valves for the exhaust, how much does that affect the carbs

The choke makes the fuel/air mixture become more fuel-laden so if you have an air leak, the choke compensates for the leaking extra air by enrichening the mixture. But here's a question.

When you cranked that idle thumbwheel in all the way, did you still need to have the choke on to keep the bike alive?


Here's what I mean.

If you screw the thumbwheel in, the revs will start to rise. You can get the motor revving up to 3000rpm usually quite readily by turning in this idle adjustment thumbwheel.

If you really go to town on the thumbwheel like that, so that you can hear the revs really rise into the 2k's and 3k rpm's, if you try that -- do you still need the choke on?

If the answer is 'yes' then you might have an air leak.

Did you put the pods on or was the bike running fine with the pods on before, and this 'won't run without choke' only started after the carb clean?

If you had it running with the pod filters before the carb clean, and in reading your 1st post: "It ran and drove fantastic so i took everything apart mostely for cleaning, put it back and now..
It runs great until you close the choke, or if I put it in gear and let the clutch out it boggs down and dies under 3000 rpm"......

then it does sound like the 'choke on or engine dies' problem only began *after* the carb clean and re-install.

On the rubber-ish intake manifold between the carbs and cylinder are rubber plugs and if you remove the plugs, there are nipples provided for the mechanic to hook up a vacuum carb sync tool. If one of the plugs is cracked or missing, could be an air leak right there.

If you don't have the carbs pushed all the way as deep as possible into those intake manifolds and/or the clamps there aren't tight, that could be another source for an air leak.

And if the prior owner who removed the stock fuel injection that came on the bike did not change the head to a standard 'carburetor-not-fuel-injector' head -- then check the block-offs that are probably there to plug the holes where the fuel injectors used to be.

And get the bike started and spray some Wd-40 on those intake manifolds -- if the engine revs change then yep it means you probably have an air leak.

Can you take a photo of your motor on both sides of the carbs and cylinder head, preferably with the gas tank off?

OK... it had pod filters when i got it,, thumbwheel all the way in it went to 3000 but still needed the choke. I also sprayed everything and could not find any air leakes. it has the fuel injected head still but the holes are plugged with some kinda super epoxy, they didnt leak. The two outside nipples for the sync tool are hooked together and go to the air valve thats connected to the (exhaust) valve cover. the two inside are hooked together, this is how it ran before.

OK... it had pod filters when i got it,, thumbwheel all the way in it went to 3000 but still needed the choke. I also sprayed everything and could not find any air leakes. it has the fuel injected head still but the holes are plugged with some kinda super epoxy, they didnt leak. The two outside nipples for the sync tool are hooked together and go to the air valve thats connected to the (exhaust) valve cover. the two inside are hooked together, this is how it ran before.

the pictures didnt work im gonna have to figure that out

I have a bike (not a Kaw) with a vacuum-activated petcock. The prior owner put the petcock on 'Prime' and hooked in a fuel flow switch, thus defeating the vacuum activated functioning of the stock petcock.

He then plugged the nipple on carburetor #3 where the vacuum line to the petcock was normally connected.

If he had *not* plugged that nipple on carb #3, boy would the bike have an air leak.

(ps. I'm yet to get around to returning the bike to the stock petcock situation, I don't yet know why he decided to bypass the vacuum petcock this way but I'm sure I'll find out soon enough. I'm assuming the petcock leaks and he was unaware of petcock rebuild kits, and added the 2nd fuel flow switch to positively turn the gas flow OFF from the tank.)

Anyways, this other bike I have came to mind here -- is your vacuum-activated petcock hooked up and functioning?

Man, if you need full choke with the idle speed thumbwheel turned in all the way it really sounds like a leak.

So here's another question.
Pull all 4 spark plugs -- are they:

- whitish and looking like they ran super hot, with very clean white ceramic and metal bits?

- light brown or golden brown ceramic?


- dark, sooty, black or oily?

Pictures of the plugs would help but just know which of the above description fits your plugs will help too.....

Z1class wrote:

I have an 80' z1classic that has carbs now. Looking in the clymer book they look like the diagram for 77. they have air mixture screw no fuel mixture....

'77KZ1000 oem carbs are Mikuni 26mm manual slide with bottom located pilot fuel mixture screws.

There are of course also other Mikuni manual slide carb designs with a side located pilot adjuster air screw.

[Click on image to enlarge view.]



Good Fortune!

Anybody still readind this? I got my bike fixed enogh to ride the
Fuel levels in the float bowls were uneven too low and too high
Now I feel like a dummy. I cant turn the choke allthe way off either
Only half, but it ran good at all rpms. After warming up it idled at about 3ooo with the thumbwhell all the way out. When I got back I used a laser
Thermometer on the exhaust. 1, 3, and 4 were 90 degres and
#2 was 160. Does that meen that cylinder is running lean, valve clearance
And compression, are good. If so will a vacuum sync fix that
I dont want to change one carb without syncing, anymore advice is appreciated

this may sound too simple but have u checked the condition of ur gas tank, ???? rust, crap etc, just a thought

not that this will fix it but , start from their, clean, bench sync, valve adjust, then start tryiong to diagnose,
you're chasing
be methodical