77 kz650 racing idle

So I’ve got the bike back together after a bunch of work. And it’s running clean except that I’ve got a bit of a hanging idle when blip of throttle or ridiing and of throttle. I’m thinking I bench synced the carbs too far open. I’m gonna go back and re sync. My main question is, if in theory one is too bench sync .5mm-1mm wire with throttle stop screw set centered. Wouldn’t it work the same if your settle the carb slides gently closed with the throttle stop screw are out 3/4 of its position work the same??

thanks for the space and the jnput
andrewR

Also, I’m fully stock jetting and needle position. I’ve got K&n drop in filter, stock air box and 4-1 Mac exhaust. Runs smooth thru the rpms except if I grab full throttle I get a bog.  Up the main jet 2.5 or 5 ??

thanks again guys

Bench sync is to get the carbs close so the engine will start. It’s also to get the idle speed screw into the correct range for proper idle adjustments. Your correct in theory if you lower the slides by the idle speed screw you have effectively bench sync’d them with a smaller wire. You hanging idle is not from a bench sync with a wire to dig. It’s a sign of a lean mixture. You can try adjusting the pilot screws. If they are between the air box and slides they adjust air. Turning them in will make your mixture rich, less are added to fuel. Out will be lean. If they are between the slid and the engine they adjust fuel. Out more fuel, rich, in less fuel, lean. 

I have fuel mixture screws.

My reasoning behind thinking i need to reset my slides lower is that I don’t have any more out adjustment on the throttle stop screw . Which tells me the carbs slides are set too high and/or didn’t set my throttle set screw close
enough to center for adjustment range

Open this manual and read pages 17-19. 

www.kzrider.com/modules/ServiceManuals/K...Service%20Manual.pdf

The first step to a bench sync is to adjust the idle adjustment screw to 1.6 to 2.0 mm gap between the throttle pulley and the stop bracket. 

 

You will need to do a final vacuum sync. That is described on pages 19-20. 

Id adjust the idle pilot screws to get the best idle, then vacuum sync. Readjust pilot screws and idle speed. If your still lean with hanging idle then you need to find air leaks. Most common is the carb holder boots. 

Thanks @mikaw.  I get on it this evening. 

Any insight to main jet issue?. I’m gonna order up 102.5 and 105s.  Stockers are 100s

I’ve got new carb intake boots on the head side and on air box side with new clamps and springs

You need to read the plugs to find out what you need to change or adjust. Start here

www.dragstuff.com/techarticles/how-to-read-plugs.html

Then this is a great tuning guide.

www.vintagebikebuilder.com/mikuni-tuning-and-jetting-guide.html



 

Hanging idle is often a symptom of cracks in the rubber carb boots.  And spraying stuff on them doesn't always find the leaks.  If the boots are original and/or hard I'd go straight towards replacing them.

Just to clear up. It’s a hanging idle/rpm not racing

Also the carb intake boots are brand new as are the airbox horn rubbers

will perform another bench sync and vacuum sync this week. I think the slides are too high or at least one is, like they aren’t closing all the way off throttle

A good idle is between 900 and 1100 RPM. If your bike will idle somewhere close to that and you can turn idle speed screw down to get it below 800 you should be pretty close. Just because your carb holders are new doesn’t mean the are sealed up. Cheep $25 eBay are must that, cheep. You need a good set from a good company.