Carb adjustment order

Just finished warming up my 1976 KZ900 and she was running a bit rough. The top end has been completely rebuilt including Pistons, rings, carbs, timing chain, carbs, etc. Went with pod air filters and got rid of the air box as well as a four into two baffled Jardine header. When I pulled the plugs to check them out they were all a very sooty dry black. Air screws on carbs are set to 1 1/4 turns out, carbs rebuilt with factory jetting, timing set with strobe light and is bang on and carbs synchronized using carb stix. Can it be the needle/ clip position? Right now it is set in the middle....any suggestions?

Why'd you get rid of the air box? 

Are the jets all stock sizes or were they changed by the PO?

Did you bench sync the carbs first? You may have set them all to being the same with the carb sticks, but if you didn't bench sync them, they may all be open too much which could lead to a rich condition. 

1 1/4 turns on the air screws is a good starting point, but you'll send to go through each one individually to set them up for best idle. Take your time with this. 1/8 turn at a time, then give several seconds to listen for a change. 

I'm not sure of the top of my head, but pretty sure the needle clip should be 4 from the top.

Have you checked the bowl fuel levels. Too high bowl fuel level will also make for a rich mixture. Just setting the air screw to factory settings is not setting the tuning right. You need to colour tune also.

Oh and put the airbox back on and bin the pods. If they are cheap pods there is a fairly high probability that they are blocking the pilot circuit air intake which will also obviously make for rich mixture.

To supplement what the others have said, the bike won't run even close to properly with pods and the factory jetting.  The mixture will be drastically lean and no amount of messing with the pilot air screws will fix that.

And as the others have said again, the $10 generic pods are junk, so if you have your heart set on running pods be sure yours are a set of real K&N's or pods from APE.

A rich mixture like you describe suggests a high fuel level.  You would be well advised to perform the clear tube test and measure fuel level in the float bowls and then adjust the floats as necessary to bring the levels in spec.  If adjustment doesn't work they you will have to buy new float valves and maybe even floats.

Another possible reason for running rich are leaking choke plungers.

There is a member here that rebuilds choke plungers and he also sells an air correction jet which makes the carbs easier to tune if you are running pods.  These parts are not cheap but they will likely save you some time and headaches.  

With pods and stock jetting you should be running lean.
As already mentioned DO NOT use cheap Emgo, Moxi etc pods as these are restrictive and cause rich running and loss of power.
With quality pods ( K&N , APE etc ) you should fit air corrector jets, go up on the mains a few sizes and leave all other settings, needle in middle position, pilot jet  etc stock.
If rich running persists and float heights etc are correct then worn plungers are becoming a big culprit due to the nitrile seats degrading with ethanol along with normal age hardening.
I can provide the Air jets and repair the worn plungers with ethanol resistant Viton seats if you require them.

 

Not sure what you mean by Bench Synking the carbs. Is there a procedure for this?

Fuel bowl height was checked on the bench for all 4 carbs and all was within spec. 

Thanks for the info. Lots of different opinions so I guess I got some good advise to start..........

wrote:

Not sure what you mean by Bench Synking the carbs. Is there a procedure for this?


Excuse the lack it specs in this reply as I don’t have a manual to quote them correctly.

The bench sync is performed to get the carbs to a baseline setting. If I’m correct you abjust the idle speed thumb screw to X mm. Then with the carb tops off you use a X mm size wire gauge and adjust all slides up or down to get a smooth friction fit on the wire gauge. It is placed between the bottom of the slide and the bottom of the carb throat. This sets the carbs back to factory specs, and is close enough to allow the engine to start. Then a vacuum sync, pilot screws adjustments, and final idle RPM setting is made. If a bench sync is not done the idle adjustment screw may be out of range and not allow for proper idle RPM. 



 

wrote:

Fuel bowl height was checked on the bench for all 4 carbs and all was within spec. 



 

Did you use the clear tube method to check float levels. 

I used the clear tube measurement procedure when the carbs were on the bench after I did the complete rebuild on the carbs.

Should this check be done on all carbs with the bike on the center stand as well ??