TOPIC:

Over the years there has been much discussion regarding the apparent difference in required "turns out" of the idle-air screw setting. The manual states a significantly lower number of turns (1-3/4) to the generally accepted 3 to 5 turns that is actually found to be necessary for correct idle operation.
Although the practical settings required have never been an issue, the answer to the question has remained unanswered.
I'll suggest the following theory and would like others opinions. This discussion won't change our procedures; it's simply a discussion for the curious.

IF during the development of the carburetors and initial adjustments to meet emission standards (I purpose) that the idle-air screw never had the short tapered "needle" on the end of the idle-air screw. Perhaps then, during further refinements it was discovered that emissions standards were not being met consistently it was at this time the stubby "needle" portion was added to provide a finer and more sensitive range of adjustment. Conversely the addition of the short tapered "needle" to the end of the screw may have been an after thought simply to give a finer and greater range of adjustment solely for tuning purposes.

With no tapered needle extension the otherwise stubby end of the needle would act more like a faucet with the screw-end simply opening and closing off the idle-air port in the bottom of the threaded cavity. The range would be very short, perhaps accounting for the manufacturers suggestion of 1-3/4 turns. The adjustment would be very sensitive in this case. Now add the tapered extension which would extend into the fuel/air port at the bottom of the needle port. It creates a restriction to the fuel/air delivery which in turn would account for the needle needing to be turned out further to the commonly accepted 3+ turns.

It would be interesting to have a sacrificial needle to experiment with. Only one would be required to test this theory. By removing the tapered portion and installing it in place of a "standard" needle the affect could be readily witnessed. On a well tuned engine the sensitivity of modified idle-air screw could easily be determined as any changes to a setting will normally have an immediate and discernible affect on the idle quality, on the one cylinder.

Just a thought !

I am still coming to terms with this also. I started with 3 to 3-1/2 turns and since then I purchased a colortune to set the idle screws. According to the colortune they are now set at 1-3/4 to 2 turns for the blue butane color. I am still having problems getting it to idle nicely and it is currently a work in progress.

This is the carb kit I installed which was more or less the same as before except for the starter plunger (I installed the original starter plunger)

I'm kind of in the same boat. I initially set my 1980 screws at about 2.5-3 turns out, and while at idle she ran incredibly rich. It wasn't the float height, because I tightened a couple of the screws up a turn or two and managed to kick one of the shared cylinders closer to a nice tan plug color, while the other (on the same carb) was still rather wet. I started having other issues before I could tune it up even more, but I have a feeling that when all is said and done most of my idle screws are going to be in the 1.5-1.75 turn ranges.

Now, I'm not saying this is "correct". You set the screws to where they work best for you. This is just where mine happened to end up.

in all fairness to Scotch I think we all need to realize that Scotch has attempted to explain why we have a discrepancy in the initial idle air screw settings reported on the numerous different posts regarding this topic and I thank him for that. Obviously, if there are two different styles of air bleed screws out there, we need to realize that and understand just how the different screws affect the various different settings required to achieve what tuners describe as "lean best mixture" setting. One of the biggest problems we (kz1300 owners) have is trying to set up 6 carburetors on one engine (and I know some out there are saying no, there only 3 carbs) but in fact we have 6 separate carbs sharing 3 common float bowls. If an adjustment is made to 1 air bleed screw it only affects 1 cylinder.

We could banter this topic to death and never come up with a concise answer to the issue. There really is only 1 way to set up the idle air bleeds and know you "in the ball park and that's the Colortune option. It will give you an opportunity to "see" the flame front and you'll be able to adjust the air bleeds based on the color of the flame in each of the cylinders. Where the air bleeds end up, who cares. The goal is to have the cylinders all burning with a nice blue flame which is neither lean nor rich. Obviously if the engine won't run you can't Colortune it so you need to start with an initial setting. Most air bleeds with the tiny little pin on the end will want something in the 3to 3-1/2 turns and if by chance you have the stubby air bleeds you'll want to start on or about the 1-1/2 to 1-3/4 turns out.

I have purchased an O2 monitoring system to be mounted on my ride and even it will only be able to tell me what the "average" of all the cylinders is running at. At best I'll be able to jet the carbs and set the throttle needles based on the "average" O2 available in the exhaust pipe.

Bottom line- Get yourself a Colortune kit. It's an invaluable tool and you won't regret the purchase. You'll never get the carbs set right without it, at least not on a 6 cylinder engine with 6 carbs.

When the KZ1300's for the North American market were being produced, it was my privilege to work in Japan. The 1979 KZ1300's had a port on each exhaust header just after the pipe exited the head. These ports were capped off with screws. I owned a new 1979 U.S. export model while in Japan.

It was always my guess that the 6 ports on the exhaust headers were to accommodate a wide band O2 sensor to allow setting the idle screws individually for each cylinder, at the factory. I could be wrong.

My short lived '79 also had the ports on the headers and I thought the same thing ! It's interesting to here there are those who find the manuals setting closer to what they find best. Thanks