Slight hanging idle when hot.

[Dolomite_]

I went for the 2nd break in run yesterday and it was mostly fine, just a clutch adjustment at first but after it was hot when stopped at traffic lights in 1st, and with the clutch in the idle seemed to hang at 2k - 2.5k rpm but when closed that the throttle that extra bit from its natural resting position it then started to fall back to what it should be idling at.

Is there anything I need to check/adjust? Does the throttle linkage at the carbs need to be adjusted so it closes more? It appears to be fully closed because the extra bit I close the throttle just fully slackens the throttle cable.

[K2-K6]

Firstly, try putting more slack into throttle pull cable if there's adjustment available.

The throttle slides should never be "hanging" on that cable, clear slack should be there.  The slides should only sit on their mechanical operating mechanism and be completely independent of the cable when you release the grip.

There's diagram in manual for setting that twistgrip movement to reference.  Also try turning steering from lock to lock while idling, it should not affect rpm at all.

[McCabe-Thiele (Ted)]

As K2-K6 (Nigel ?) has said when the throttle is closed it should go back fully to the idle stop screw on the main bracket.
It is important that both cables are correctly adjusted as per the manual.

It also helps if the angles on the outer cables are a nice curve into the front frame area- these are adjustable at the handle bars.

The original route of the throttle cables is on inside of the headlamp bracket - as I have fitted a non-standard headlamp my cables run on the outside of the forks.

cable routes by Macabe Thiele, on Flickr
.

[Alexrayz]

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


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[Martin6]

If it hangs after you've adjusted the throttle, check for a leak in the carb to head rubber manifolds.

[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)]

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


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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.