SOHC.co.uk Forums > CB750

Hanging idle please help

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blackeagles:
i don't have that type of carb so cannot test however this video clip (first couple of revs or so) seem to indicate that the carb should snap shut

https://www.bing.com/videos/search?q=honda+cb750+k2+carb+setting&&view=detail&mid=F17208F1C8D28AAFB071F17208F1C8D28AAFB071&&FORM=VRDGAR&ru=%2Fvideos%2Fsearch%3Fq%3Dhonda%2Bcb750%2Bk2%2Bcarb%2Bsetting%26FORM%3DHDRSC3

Wenman:
Mine operate the same as that and they do slam shut when opened up anymore than 10%.

It’s only occurring when I apply a very small amount of throttle.

I posted a video of it earlier in the feed and you can see where the hang up is

If I open the throttle anymore than 10% the weight and force of the spring slams them shut.

If I apply a very tiny amount of throttle that closing momentum created by spring and the weight etc isn’t present so they are closing but very slowly?

JezzaPeach:
I’m clutching at straws here but could there be a little suction pulling the needles up in their holes? If that’s not nonsense, maybe allowing more air via the pilots (1/4 turn anti each) might help.

blackeagles:
so your saying with the engine off they snap shut but with it running thye shut slowly if slightly activated but ok at a larger movement of the throttle.  presumably with cable on and off and if you press them down either running or not they close 'correctly'.  only thing i can think of if everything is running freely it could be the vacuum pressure in the venturi acting against the return spring - is the spring the correct poundage for this carb?

Wenman:

--- Quote from: jeremypeachey on July 14, 2020, 01:43:09 PM ---I’m clutching at straws here but could there be a little suction pulling the needles up in their holes? If that’s not nonsense, maybe allowing more air via the pilots (1/4 turn anti each) might help.

--- End quote ---


I understand your logic here, however if the lifters were closing fully and the revs hand that could be a cause.

The revs hanging is being caused by the lifters and subsequent sliders are not falling quick enough

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