SOHC.co.uk Forums > CB750

Warm up time

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Simon46:
My 78 k8 takes about 6 mins to settle itself down before its rideable.is that normal? The idle speed has to be lowered as its idling at 2500 rpm when it's hot. Any ideas?

Bryanj:
That one has the lean running PD carbs i think so that sounds about right

K2-K6:
As above,  they do take a while to get warmed to a normal throttle response. 

The cold running on full choke and fast idle is listed by Honda at 2750rpm plus or minus 750rpm.

The hot idle you may have a problem with setup though. The routine will never adjust the no2 carb when synchronising the slides.  This one stays in the same relative position in regard to the throttle lift mechanism and could be where your problem lays.
Normally you'd adjust 1,3 and 4 slides to bring parity with no2 during setup,  but if the no2  carb has been set incorrectly  it will give an unrequired offset to the whole carb rack.

To get out of it, you'd have to reset no2 so that when the main idle screw is moved it will have the range to bring that no2 carb slide fully closed and up to a reasonable idle.  Only then can you bring the other three to match it.
This should give you normal hot tickover ability and range.

Bryan has a really good routine to set the carbs on a bench and get them on track for a good start point,  may have to search on here for it.

Simon46:
Thank you. When I got the bike all jets were blocked with brown crud and the idle screw was wound in fully. I've had tank and carbs cleaned from the1990s petrol which took 2 weeks so adjustments are required I expect.

Erny:

--- Quote from: K2-K6 on October 28, 2018, 10:55:24 AM ---...

Bryan has a really good routine to set the carbs on a bench and get them on track for a good start point,  may have to search on here for it.

--- End quote ---

Can you advice where to find routine you mentioned? My K7 has the same sympthoms

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