Erratic idle / fuel mixture

Hi all,

I'm having some trouble with my '77 kz400 deluxe. It recently failed emissions, so I'm trying to dial in the fuel mixture and idling speed.
Before the test, I went through and cleaned the carbs and fuel tank, but I did not touch the idle mixture.
Since then, I have the pilot screws set at about 1 and 1/2 turns out. The bike will idle around 1100-1500rpm, but it will rise to 3000rpm sporadically, hang there for a few seconds, and slowly drop back down. Adjusting the throttle cables has no effect on this.

I guess my first question is, what can I do to make sure my bike passes emissions on my retest? Am I setting the pilot screws correctly?

And what can be the cause of the erratic idling?

Thanks

What are you using for air filtration? Have you checked your carb holders for vacuum leaks? Ed

The air filtration is all stock. (airbox with new filter). The previous owner fashioned some air intake boots from rubber tubing that seem to be doing the job.

I haven't checked the carb boots (engine to carb) for leaks. I have replaced one that appeared to be leaking fuel; they seem to be working well now, but i'll check for leaks.

I'm a little confused about adjusting the pilot screws... The manual says to adjust the pilot screws to get the highest idle speed and then adjust the idle screw to settle around 1200rpm. Others have told me to screw in the pilot screws as far as they will go while the engine still turns over smoothly. This is my main concern as my emissions readings were almost double the legal limit... Can anyone clarify this process?

Thanks

For sure check for carb holder leaks. Temporarily idle the engine as possible when checking, that will make it very easy to tell if carb cleaner is being drawn through the leak because the engine will probably stall. With a high idle engine sucks too much air though the slides to make the test conclusive. Leaky carb holders will make for erratic idle.

Also do a clear tube test to ensure the fuel level in the carb bowls is not too high. If it is high it may account for the failed test as excessive fuel may be sporadically sucked into the cylinders. Ed

Thanks Ed.

I wasn't really looking forward to removing the carbs again, but I've had a feeling that the fuel level would give me trouble.
My manual doesn't give an ideal fuel level measurement.
I've heard that 2mm below the carb body is a correct level? Does this mean just below where the float bowl joins to the carb body?

My manual shows the correct fuel level to be 2.5 - 4.5 mm below the joint where the carb bowl mates with the carb body. The clear tube test can be done with the carbs on the bike. Ed

Thanks Ed, I'll see if I can pick up some clear tubing and fashion something to measure the fuel level tonight.

I checked the fuel levels last night and they are within spec. A little on the low side, even.

Sorry if I missed it, but did anyone verify the pilot screw adjustment process?
I'm taking her in for emissions again tomorrow; I wanna make sure it's running as lean as possible

Thanks