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77 kz650 racing idle

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25 Apr 2021 12:36 #847422 by 504Ghost
77 kz650 racing idle was created by 504Ghost
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

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25 Apr 2021 12:59 #847424 by 504Ghost
Replied by 504Ghost on topic 77 kz650 racing idle
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

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25 Apr 2021 13:21 #847427 by Mikaw
Replied by Mikaw on topic 77 kz650 racing idle
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. 

1976 KZ 900 A4 kzrider.com/forum/11-projects/613548-1976-kz-900-a4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.

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25 Apr 2021 13:31 #847429 by 504Ghost
Replied by 504Ghost on topic 77 kz650 racing idle
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

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25 Apr 2021 13:51 - 25 Apr 2021 13:52 #847431 by Mikaw
Replied by Mikaw on topic 77 kz650 racing idle
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. 

 


1976 KZ 900 A4 kzrider.com/forum/11-projects/613548-1976-kz-900-a4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.
Last edit: 25 Apr 2021 13:52 by Mikaw.
The following user(s) said Thank You: 504Ghost

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25 Apr 2021 14:01 #847433 by Mikaw
Replied by Mikaw on topic 77 kz650 racing idle
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. 

1976 KZ 900 A4 kzrider.com/forum/11-projects/613548-1976-kz-900-a4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.

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25 Apr 2021 14:02 #847434 by 504Ghost
Replied by 504Ghost on topic 77 kz650 racing idle
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

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25 Apr 2021 14:03 - 25 Apr 2021 14:03 #847435 by 504Ghost
Replied by 504Ghost on topic 77 kz650 racing idle
I’ve got new carb intake boots on the head side and on air box side with new clamps and springs
Last edit: 25 Apr 2021 14:03 by 504Ghost. Reason: Misspelling

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25 Apr 2021 14:44 #847441 by Mikaw
Replied by Mikaw on topic 77 kz650 racing idle
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



 

1976 KZ 900 A4 kzrider.com/forum/11-projects/613548-1976-kz-900-a4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.

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25 Apr 2021 14:49 #847442 by Nessism
Replied by Nessism on topic 77 kz650 racing idle
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.

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26 Apr 2021 07:39 #847481 by 504Ghost
Replied by 504Ghost on topic 77 kz650 racing idle
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

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26 Apr 2021 09:02 #847487 by Mikaw
Replied by Mikaw on topic 77 kz650 racing idle
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. 

1976 KZ 900 A4 kzrider.com/forum/11-projects/613548-1976-kz-900-a4
1976 KZ 900 B1 LTD
1978 KZ 1000 B2 LTD
1980 KZ 750 E1
Kowledge Speaks, But Wisdom Listens.
Jimi Hendrix.

Please Log in or Create an account to join the conversation.

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