NC31 1992 Workshop Manual

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Cockahoop
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NC31 1992 Workshop Manual

Post by Cockahoop » Sun Dec 13, 2020 2:37 am

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

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Speedy
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Re: NC31 1992 Workshop Manual

Post by Speedy » Thu Dec 17, 2020 12:14 am

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.
When the mind is relaxed, the body will go faster! 8-)

untonyto
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Re: NC31 1992 Workshop Manual

Post by untonyto » Sun Jan 17, 2021 6:59 pm

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.

Cockahoop
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Re: NC31 1992 Workshop Manual

Post by Cockahoop » Sun Jan 24, 2021 8:07 am

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.

Cockahoop
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Re: NC31 1992 Workshop Manual

Post by Cockahoop » Sun Jan 24, 2021 8:11 am

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


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