SOHC.co.uk Forums > CB350/400

Occasional stall it idle...

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Mikep328:
Once in a while my 400F will be idling smoothly at 1100-1200 RPM and suddenly quit.  On pressing the start button it will restart instantly and idle smoothly once again.  Some days it will do the "quit while idling" and other days it won't.  When it occurs, it might do it after idling for 10 seconds or it might do it after idling for a minute or two . Or, more often, it never does it at all on a ride.  It's not a problem since the bike restarts before I can even remove my finger from the start button.  But I'm a bit anal that things should work as they are supposed to work!  I can't figure out what would cause this, especially the very erratic nature of the occurrence...

K2-K6:
To get a complete and instant stop, that suggests power supply as reasonable suspect. Do the lights etc go out too when it stops.

Obvious things like security and tightness of battery connection along with other terminals generally around the bike. Sometimes something may have been victim to general vibration.

I had similar recently on my 80s Honda, with ignition barrel position being sensitive to any slight misalignment from exactly centre. Felt like it was "hanging " slightly on detent positioning. I used a product I've got from Land Rover to spray into the lock barrel via key slot, which was very effective in making it wok smoothly with more free engagement of detent hold.
The product is something similar to a very thin chain lube, some light grease, ptfe, alcohol to propell into the nooks and crannies, usual type of mix that should permeate and then stay put after application.

The type of contact blocks on the back of these ignition switch can also get a bit gummed over time, that to provide patchy inconsistent contact too.

Mikep328:
THANKS!!!  Hadn't thought about the ignition switch.  I'll check that out tomorrow. 

Oddjob:
In my experience it’s normally a carb problem. The tickover is too high btw, 1000rpm is the norm and at that speed it will happen more often, which is why it’s set at that speed. It highlights any problems. Might be a partial blockage in the idle circuit, might be a carb balance problem or might even be a mixture problem or float height.

Mikep328:
Interesting re idle speed. On page 6 of the CB 350/400F service manual it states idle is set to 1200RPM.  Was there a bulletin or something that revised it to 1000 RPM or have I missed something elsewhere in the service manual re idle speed (that's certainly quite possible!!!)?

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