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Discussion Starter · #1 ·
I have an 1981 kz440 with the original carbs, original airbox, and air filter. I rebuilt both carburetors, adjusted the valves, cleaned the gas tank, put a new battery into it, changed the oil, new starter, it also has new oil Valve seals. I got the bike from a neighbor. It was just sitting in his yard, he said it just needed a starter to run. It will fire up and idle, but when given gas around 2,000 rpms it starts to sputter out and eventually dies. I have adjusted the floats, and adjusted the fuel mixture screw. I'm stuck, I've worked on this bike almost all winter and can not figure it out. Any help would be greatly appreciated.

I have the original service manual that I have been using.
 

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Welcome to the forums UtaMaskmaker,
We can try to help you out, but first we will need more information:

Were the carbs completely stripped down, each jet removed, cleaned and visually inspected as being totally clean?
This is critical as even the smallest blockage can cause the problems you describe.

Did you inspect the diaphragm for the smallest of tears or pinholes?

Are you using fresh gasoline?

Are you doing your testing with the airbox connected?
 

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Discussion Starter · #3 · (Edited)
Welcome to the forums UtaMaskmaker,
We can try to help you out, but first we will need more information:

Were the carbs completely stripped down, each jet removed, cleaned and visually inspected as being totally clean?
This is critical as even the smallest blockage can cause the problems you describe.

Did you inspect the diaphragm for the smallest of tears or pinholes?

Are you using fresh gasoline?

Are you doing your testing with the airbox connected?
I completely disassembled the carbs, cleaned all jets with cleaner, compressed air, and made sure every hole was clear with a small piece of wire. The carbs were also cleaned with an ultrasonic cleaner.
I have checked the diaphragms, they are both in good shape, no holes/ stretching. And I am doing my testing with the factory air box connected. And I am also using fresh gasoline.
 

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Ok it sounds like you did a good job on the carbs but FYI the wire test for jets confirms you have a hole at least the size of the wire but does not confirm the jet is totally clear of a blockage. This is why holding it up to a bright light with a magnifier is the best final check.

Did you happen to record the sizes of the jets, or any markings on the needles when you had the carbs apart? which needle groove was the clip set in.

Are the carbs synchronized? Are the spark plugs new?
 

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Discussion Starter · #5 ·
Ok it sounds like you did a good job on the carbs but FYI the wire test for jets confirms you have a hole at least the size of the wire but does not confirm the jet is totally clear of a blockage. This is why holding it up to a bright light with a magnifier is the best final check.

Did you happen to record the sizes of the jets, or any markings on the needles when you had the carbs apart? which needle groove was the clip set in.

Are the carbs synchronized? Are the spark plugs new?
I will try holding it up to a light. All the jets and carb parts are stock.
The floats are set, and everything seems to be functioning as intended.
I'm not sure which groove it was in, I will have to check.
There are two new spark plugs, and the carbs are bench synced, I have a digital syncer but I haven't done that yet, since I can not get the bike over 2,000 rpms.
 

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Ok, so if the carbs are clean, stock jets, everything adjusted properly, and if it is getting enough air (clean filter) and with new plugs and fresh gas, it should rev up. I am assuming that there is no chance valve timing is off. When was the last time valve clearance was checked?

Is there any chance that a rag was left in one of the cylinder intakes? It would not be the first time this has happened.

If you do remove the carbs, I would do the following:

1) check the cylinder intakes for an obstruction
2) examine all jets (pilot jet in particular) with a light source that allows you to see a full, round, unobstructed hole.
3) make sure any tiny passageways within the carb body are clean.
4) note the clip groove of the needle and verify the needle and needle jet are stock.
 

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Discussion Starter · #7 ·
Ok, so if the carbs are clean, stock jets, everything adjusted properly, and if it is getting enough air (clean filter) and with new plugs and fresh gas, it should rev up. I am assuming that there is no chance valve timing is off. When was the last time valve clearance was checked?

Is there any chance that a rag was left in one of the cylinder intakes? It would not be the first time this has happened.

If you do remove the carbs, I would do the following:

1) check the cylinder intakes for an obstruction
2) examine all jets (pilot jet in particular) with a light source that allows you to see a full, round, unobstructed hole.
3) make sure any tiny passageways within the carb body are clean.
4) note the clip groove of the needle and verify the needle and needle jet are stock.
I checked the valve clearance after I replaced the valve oil seals, and they are supposed to be .17mm -.22mm so I set them on .19mm. This was a couple weeks ago. Since then I have been trying to figure out this problem, so I have cleaned the carbs several times. Tonight I'll disassemble the carbs again, and check the valve clearances again.

Sometimes it seems to run better than others. It'll normally start sputtering out around the 2,000 to 3,000 rpm mark, then die if throttle is not released. But if you release the throttle, it'll die as well.

I've had the carbs apart several times since the rebuild, and I never noticed anything in the intakes, but I'll double check. Weirder things have happened.
 

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Do you have any other history that might be helpful? Did the bike sit outside for any length of time? How many kms are on it? Are you the 2nd owner? What other maintenance or repairs did previous owner do?

I am thinking you should do a compression check to rule out valve timing, bad valves, rings, head gasket etc.
 

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Discussion Starter · #9 ·
Do you have any other history that might be helpful? Did the bike sit outside for any length of time? How many kms are on it? Are you the 2nd owner? What other maintenance or repairs did previous owner do?

I am thinking you should do a compression check to rule out valve timing, bad valves, rings, head gasket etc.
It was sitting on a property a buddy bought so he gave me the bike, I have no previous knowledge of it, besides it ran before the starter stopped working. I have ran a compression check. When I replaced the valve oil seals I replaced the head gasket.
 

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Also, forgive me, but I don't have a manual for your bike and I just realized it does not have electronic ignition. Have you checked ignition timing, point gap and that the mechanical timing advancer is actually working.
 

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Excellent. Are you able to check spark advance with a timing light? Again without a manual I don't know if you have strobe light timing marks on the bike. I would not put this test high on the priority list yet though. Compression is the big issue right now.
 

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Discussion Starter · #17 ·
I'm no
Excellent. Are you able to check spark advance with a timing light? Again without a manual I don't know if you have strobe light timing marks on the bike. I would not put this test high on the priority list yet though. Compression is the big issue right now.
I'm not sure if I can check with a timing light. I am planning on checking compression again tonight after work
 

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Discussion Starter · #19 ·
I went to do my compression test and when I took the spark plugs out they were black as sin.

I still did the compression test which was as followed.
Right without oil: 80psi
Left without oil:90psi
Right with oil: 90psi
Left with oil:91-92psi
 

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Ok, I would forget about carbs or ignition for now. Your number one problem is lack of compression. I don't have a manual for this bike but I would guess it should have 140-150 psi.

The first thing I would do before tearing it apart is to triple check the valve timing and the valve clearances. Valve timing being off by only one tooth can make a huge difference.
 
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