SOHC.co.uk Forums > CB350/400

Slight hanging idle when hot.

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Mikep328:
Don't know if this is ever an issue with these engines but on my Norton Commando if the centrifugal ignition advance mechanism was worn or needed cleaning/lube/new springs, the weights could stick at a higher RPM position.  This causes a very fast "idle" when the throttle is closed.   Then, some period of time after closing the throttle, the weights would slowly return to the correct idle position which would then reduce the RPM. 

Again, don't know if this can be a problem with these engines but I worked through this on my Norton some years ago - fooling with cable length/carb settings until discovering it was the advance unit causing the fast idle! ;)

McCabe-Thiele (Ted):

--- Quote from: Alexrayz on July 13, 2024, 06:05:59 PM ---Speaking of that, do you have a picture of the horn area? I have removed the wire bracket thingy and cant remember how to put it back i. place


Sent from my iPhone using Tapatalk

--- End quote ---

I'm not at home today - iirc the parts book shows the clip and horn layout.

McCabe-Thiele (Ted):
Going back to "hanging idle" as well as being caused by air leaking into the induction side between cylinder head and carb could it also be associated with an over weak mixture?
What does the exhaust feel like at the silencer end is it hot and irregular?

If there is adjustment left on the main bracket stop screw to drop the idle still further - then try closing the air screws a tad on each carb. As we pretty much all understand it's tricky getting the engine to idle nicely when hot.  Before the rebuild my 500 idle was all over the place too early to say what it's like now as I haven't ridden it yet. By contrast my 400 has been good as gold.

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