Non-combustion chamber #2.

  Let me first say THANKS to all the members who have posted so much helpful information on this forum.  KZRider has been just as invaluable a tool as my factory service manual.  This spring I picked up a 79 kz650 d2 that had been sitting for 4 years.  It obviously needed a little work, but that's exactly what I wanted.  Been a slow process since the summer has been busy, but I've come a long way.
  I've got her pretty well set, with one glaring issue.  The bike starts great & runs well at idle.  After running for a minute, I check the exhaust by sprinkling water on them.  1, 3, & 4 sizzle & skitter right off, but #2 is still cold.  When I drive it, it gives little backfire pops in the exhaust from that cylinder every few seconds.  Peering in through the spark plug holes, cylinders 1, 3, & 4 have a decent amount of black carbon buildup, while #2 appears a flat brownish color.
Here's what I've done:
  I have a nice blue spark on all four (new B7ES) plugs, & have swapped coils with no change.
  Points have been cleaned & gapped,  & timing adjusted slightly according to the fsm.
  Compression is between 154 & 161 in all four cylinders.
  Valve shims have been swapped out to bring all the valve clearances into spec.
  The bike has the original airbox & the Mikuni carbs with an accelerator pump & I've cleaned & bench synced them more than once. Float levels are good, and all passages seem to be clear.
  Each air screw was set at between 1/4-1/2 turn out, I backed them out another half turn as the bike was running VERY rich. The air screw on #2 carb was seated all the way in when I first checked it.

  My gut tells me that I must have missed something in the carbs, but my head says it's clean. As much as I'd hoped to avoid it, I'm considering pulling the head to lap the valves & check out the pistons, I'm about out of ideas for anything else.

Have you checked the wet fuel height in the carbs with the Clear Tube Test?
Did you bench sync the throttle valve height?
Even though you state you've cleaned them several times, it could still be an issue. Or possibly you have a damaged jet. Someone could have been there before, and taken old jets, maybe one has been damaged from cleaning or been drilled?

Don't pull the head. If your valves, piston, or rings were bad enough to prevent #2 from firing your compression would be horrible on that cylinder.

Here's something you may have missed. The stock petcock on your bike is the vacuum type. As such, it has a vacuum line running from the petcock to the #2 carb. If the diaphragm in the petcock has a problem it can allow fuel to be sucked down through that vacuum line into #2 carb and mess up the air/fuel mixture in #2 cylinder. As a test, you may want to put a clear vacuum line in place and see if you can detect any fuel being drawn through it. Or, you may want to try plugging the tube from the petcock, putting a tight cap on the vacuum port on #2 carb, putting a new spark plug in #2 cylinder, and running the bike (temporarily) with the petcock on Prime to see if that changes the symptoms.

Of course, it also could just be a speck of crud in #2 carb even though you cleaned it, but I would look into the petcock possibility first if you have not yet done that. Ed

Well, got at the bike today. Clear tube test had shown fuel levels within specs, double checked & confirmed. Petcock is also good as it has the same issue with vacuum line capped. I believe I have confirmed that it absolutely must be the carbs, if through a perhaps unorthodox method. In an attempt to confirm that carb 2 was indeed drawing air, I stuck my hand in the airbox. To make a decent seal, I stuck my thumb in the inlet to the carbs. There was vacuum, but oddly it did not pull up any fuel like it does in in other carbs. I'm going to have to track down a diagram of the passageways in my carbs, because I seem to be missing something.

The link below has a free download of the KZ650-B1 Kawasaki Service Manual. Click on the "Regular Download" button and open with Acrobat. This is a different model bike than yours, but starting around page 133 are some carb diagrams that may be helpful. Ed

hotfile.com/dl/148056848/131ba5a/Z650_B1...vice_Manual.pdf.html

Mausyoak wrote: ... 79 kz650 d2 that had been sitting for 4 years... After running for a minute, I check the exhaust by sprinkling water on them.  1, 3, & 4 sizzle & skitter right off, but #2 is still cold... nice blue spark on all four (new B7ES) plugs... Each air screw was set at between 1/4-1/2 turn out, I backed them out another half turn as the bike was running VERY rich. The air screw on #2 carb was seated all the way in when I first checked it....

Would guess default pilot air screw position would be more like 1¼-1½ turns out from lightly seated.

Here's a cleaning technique for the carb pilot circuit to assure air-fuel mixture is reaching the carb throat from where it may be drawn into the combustion chamber.




However, regardless of a mal-functioning pilot circuit, #2 cylinder should have combustion at mid-throttle position and above where the air-fuel mixture is supposedly being provided through the needle jet.

Has the spray-sizzle test on #2 exhaust header been performed immediately after a test run at 1/2 to wide open throttle position?

Good Fortune!

Checked all the passages for the idle circuit again, & all four openings suggested by Patton's diagram are open. Though if memory serves (which it rarely does), I'm not sure that the outlet was spraying carb cleaner or just leaking, so there could be some partial blockage. Life interfered & I had to stop in the middle of the job. As an added bonus, when I removed the air screw the o-ring pretty much disintegrated. Since some of the other o-rings are looking a little rough as well, I'll have to track down some parts & replace most of the internal rubber. It seems to me that if one piece is that bad it's inevitable that I'm going to get shrapnel from other bits as well. I'll have a more time for it tonight, so I'll go through a thorough cleaning on multiple carbs so I can compare the problem carb to the others. I've done carbs before & never had to take them apart more than once, so this is getting frustrating. Solution... start from scratch & don't assume anything was done right the first time.
As for higher throttle, the #2 header does get hotter, but not as much as the others. I'll check it again once I get the carb internals closer to my son's age rather than mine.

The #2 carb is the one that supplies the vacume signal for the petcock. Make sure you have no vacume leaks between the carb and the petcock. Also check the petcock for vacume leaks.

I had the same problem with 2 bikes. Non-working cylinder has completely closed throttle.
You have to synchronize carbs.
Bench adjustment is not substitute, it is just preliminary.