TOPIC:

Hopefully someone will be able to help me on this !

Z650B1, the carbs fitted on it just aren't playing nice. I've rebuilt them 4 times (with ultrasonic cleaning twice), and they still aren't good - I suspect a blockage, and I don't know if the main jets are right for the bike's setup (aftermarket exhaust and K&N air filters). I've got healthy spark, and I'm pretty sure the issue is the fuel system. So I'm looking to swap them out and try one of the two spare sets I've got. But each of them has issues !

Set 1 are the type with the air screw at the back (like the ones on the bike). They need a bit of cleaning, don't have jets fitted, and the floats are pretty varnished up. I've got all the bits, but would probably need to get new floats and maybe needle valves.

Set 2 have both the air screw at the back AND the pilot screw under the front of the float bowl. Who on earth thought that kind of setup was going to be fun to adjust !  But they have the advantage that they were on the bike a few years ago and ran quite well so I reckon the jets are probably the right ones and I've been able to clean them without disturbing the air screw or pilot screw settings, and I took the slides out without undoing the setting on those, either, giving me at least a starting point for how they should be. The downside to this set of carbs is that the pilot jets are quite well gummed in, so it's going to be a risk to get those out and thoroughly clean/replace them, but more importantly, the brass choke tube is snapped off on carb #4.

Do you think my instinct to work with spare set #2 is the right thing to do ?  I don't think I've got the tools or ability to replace the broken off tube, but wonder if that would actually make any difference other than on first starting up. Alternatively, I might even be able to swap out #4 carb with one from spare set #1, but am I more likely to give myself problems working with two different types of carb in the same bank ?

I can see that eventually I might even end up with three good sets of carburettors !  I'm not totally giving up with the ones that are on the bike right now, but want to put them aside for a bit to get the bike rideable so I can identify and iron out any other surprises it's got in store for me !
 

Set #2 are a Suzuki. You don’t want to mix the carbs within one rack. The choke tubes are all the same on the VM26SS, 28’s with and without pump. You could pull one from a diner set and replace. Get a propane torch heat the area around the tube and a light twist and gentle pull and the come out pretty easy. Floats unless the are brass and have holes usually don’t go bad. Float needles and seat as long as the needle is a constant taper can be cleaned and polished and reused. It is critical all passages are clear. Brake clean and careful placement of finger tips or silicone tapered plugs covering exits are the only way to assure clear  passages. You need to select one passage on all four carbs and in succession spray them, carefully watching exit volume from carb to carb and make sure all are consistent. I recently had a set of Suzuki VM26SS like yours the on carb, one passage was blocked and wasn’t able to clear. I found a stripped carb on evilbay for $20 and replaced it. If they are properly cleaned and with correct matching parts they will work. 

I have seen a couple of sets of carbs with broken choke tubes run fine, once started and warmed up. They do have an issue with starting but work fine afterwards.


There was a service bulletin on the use of the carbs with both air and pilot screws as follows

Kawasaki Service 4/600-11, 10/21/77
Recently the carburetors of the KZ650 were changed from the pilot screw type to the air screw type.
During the transition from one carburetor type to the other, several hundred units were equipped with
carburetors that had both air and pilot screws.
Units with transition carbs:
1977 KZ650B Frame # KZ650B024641-026991
1977 KZ650C Frame # KZ650C007751-010000
1978 KZ650B Frame # KZ650B027901-028701
Dealer action:
When you tune a unit with transition carburetors, turn the pilot screws all the way in. This will ensure
good idling and smooth running. The air screw setting is the same as the air screw type carburetors.
Pilot screw- Turn all the way in
Air screw- 2 +/- 1/4 turns out.
Direct from Kawasaki.

I have also had luck setting them as follows  pilot (fuel screw) 1 3/4 from lightly seated  and the air screw 1 3/8 from lightly seated

wrote:

I have seen a couple of sets of carbs with broken choke tubes run fine, once started and warmed up. They do have an issue with starting but work fine afterwards.


There was a service bulletin on the use of the carbs with both air and pilot screws as follows

Kawasaki Service 4/600-11, 10/21/77
Recently the carburetors of the KZ650 were changed from the pilot screw type to the air screw type.
During the transition from one carburetor type to the other, several hundred units were equipped with
carburetors that had both air and pilot screws.
Units with transition carbs:
1977 KZ650B Frame # KZ650B024641-026991
1977 KZ650C Frame # KZ650C007751-010000
1978 KZ650B Frame # KZ650B027901-028701
Dealer action:
When you tune a unit with transition carburetors, turn the pilot screws all the way in. This will ensure
good idling and smooth running. The air screw setting is the same as the air screw type carburetors.
Pilot screw- Turn all the way in
Air screw- 2 +/- 1/4 turns out.
Direct from Kawasaki.

I have also had luck setting them as follows  pilot (fuel screw) 1 3/4 from lightly seated  and the air screw 1 3/8 from lightly seated

Thank you. I had no idea such a Kawasaki item existed. Would these be 24’s or 26’s?

Stock on the 650s were vm24ss.  To the best of my knowledge the vm26ss that came on the kaw 900/1000 have either an air screw or a pilot screw but never both.  While the 26s that came stock on Suzukis have both.