Author Topic: CB400F cannot get it to idle properly and it is driving me nuts HELP!  (Read 1592 times)

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Offline tony67

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Hi all, this is my first post so please bear with me.
I own a '75 CB400F which I rebuilt from a barn find. These are the details:
-Engine: standard bore
-Carbs: Standard, Fitted pods, jet 85 and pilot jet 38
-Exhaust: Marving 4 in 1
-Ignition: Electronic (Kokusan from David Silver Spares UK)
I rebuilt the engine using a complete set of seals and gaskets, new piston rings, carbs were cleaned and overhauled, new standard piston rings. After all the long work and following Haynes manual instructions I cannot manage to get the engine to get a proper idle, I synced the carbs with vacuum gauges, adjusted the floats to 21mm as per manual, cleaned everything adjusted electronic ignition timing as per manufacturer's. One thing I noticed is that on one of the carbs the air-fuel mix screw will go deeper on the thread compared to the others if you screw it down to the bottom before adjusting it to 2.5 turns. I was thinking that this might cause the whole syncing to be messed up or perhaps I have a vacuum problem.
Any ideas?? This is driving me potty!!
Many thanks

Offline Hondadog

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Re: CB400F cannot get it to idle properly and it is driving me nuts HELP!
« Reply #1 on: December 15, 2013, 10:15:19 pm »
only just seen this post, your main jet should be 75 and your slow jet 40. Tons of excellent info on this site, try some of the other forums and as for Haynes manuals little book of lies try the down load manuals on this site brilliant loads of information much more informative good luck Richard :) :) 8)
1975 Honda CB4OO f my daily hack to work and alltime love. 1959 BSA M21600 sv fun to ride and a new arse change every 50 miles. Also have another CB400f engine that i wish to rebuild and build a cafe racer.