HI all – I'm new here and new to owning a CB400SF. I've just bought a modified NC31 1992 cafe racer here in Hong Kong.

It's OK overall but runs rich and lacks power mid-high end (pinking and bogging down). Also cylinder 3 downpipe is cool for a long while after starting compared to others. Seems various work is required but I can't find a workshop manual anywhere online.

Can anyone point me in the right direction please, or have a PDF they are willing to share?

Many thanks

Try this link, you can download the .pdf manual from there:
https://www.manualslib.com/manual/16545 ... -Four.html

There's also a parts manual, on the document library of this very site:
http://www.400greybike.com/files/cb400- ... -Parts.pdf

It's OK overall but runs rich and lacks power mid-high end (pinking and bogging down)

The carbs may need a clean and checking that the jets are unblocked and of the correct type/sizes.

Also cylinder 3 downpipe is cool for a long while after starting compared to others.

Swap cylinder 3 spark plug with another one, to see if it still stays cold after a while compared to the others; if it does, check that the spark plug on #3 Cyl. is sparking. If it's not, further investigation will be needed.

Good luck.

I have the same bike - 1992 NC31 - with the same issues, plus charging system issues.
No luck so far finding an English workshop manual for that model year.
So far my research has led me to order a carb rebuild kit, and also to order a new starter relay (it made sense in my head until I typed it just now), and a new modern Regulator/Rectifier.
Later on I may attempt a complete Motogadget M.Unit rewire.
So frustrated that I'm willing to try anything at this point.
So right I'm waiting for parts. Please tell us what will work for you.

Thanks for the info, Speedy.

I had the carbs cleaned by my local bike shop which made a big difference overall - bike runs much better, but still lacks power at the top end.

Workshop suggested this was likely due to various mods to convert to cafe racer style - custom air filters, exhaust etc, but also pointed out a couple of small chinks in two of the carbs, suggesting this may be impacting the vacuum seal. I’m going to try some JB Weld in the hope that creates a seal but not expecting a massive change in power output. Timing checked out OK.

Untonyto - good luck. I suggest you have your carbs cleaned and checked too as a starting point.

As well as the manual Speedy recommended, I found a Russian/English manual here (sorry for the long link, it’s from a Facebook group):

https://lookaside.fbsbx.com/file/CB400- ... 7xRH4hG-I9

It’s not a Haynes manual but better than nothing.

Sorry for the slow reply folks, haven’t logged in for a while and didn’t receive any notification email.

Sorry, and also now running on all four cylinders since the carbs were cleaned.