Honda CB400SS upgrade

[GrahamH]

I have a Honda CB400SS which is a grey import 400cc single, the SS stands for 'Standard Single'.  The engine is loosely based on the XB400R dirt bike but in a lower state of tune. It's a nice lightweight bike but not very quick so I am busy upgrading it.  First a 10.1 piston (up from 8.9:1), then the camshaft from an XBR400R and lastly a Mikuni pumper carburettor which is the usual upgrade for the XR400R, and that's where my problem lies.

The standard Kehin carb has a throttle sensor which looks to be in line with the butterfly valve in the carb so I guess it detects the position of the throttle.  It then has 3 wires which run to the CDI unit where I don't know what happens to the signal.  The Mikuni carb has no such sensor so my questions are:

1.  What is the CDI doing  with the throttle position signal?
2.  Will the engine run OK without this thing connected?
3.  Or is there another way around it or must I stick with the standard carb?

Any help/advice appreciated

GrahamH

[tevie54]

I'm pretty sure Mikuni do a direct replacement for the XR 400 which may have a connection for the wires of which you speak.
Try Allens performance products, they have a technical questions bloke.

[guest1802]

Graham,

I also have a little NC41 400ss.

And am trying to upgrade the carb, I am taking the lazy route and buying one from WM Production (Japan) which has been set up and tuned for the NC41 specifically. Can see it on the Webike / WM websites. Its not cheap, and requires you to ditch the airbox, but I'm going to try and keep it and drop the velocity stack which comes with it.

Happy to compare notes sometime on the bike. I share the shortage of information on the model with you. I do have a copy of the owner's handbook (in Japanese of course).

I am also told by my local Honda parts dealer (I'm in Singapore) that the model was made in the Thailand factory, so parts are relatively cheap and still available (must also have been why they fitted IRC tires out of the factory).

Cheers,

Dan

[GrahamH]

Hi Dan,

Check out the Yahoo forum for the CB400SS group.  They are not a chatty bunch but there is a workshop manual, wiring diagrams etc to download. 

Does your bike need the throttle position indicator from the carb? and does your intended fitment cover it?  From my limited research all the manuals say don't touch it unless you have to as it will need resetting.  So I am sticking with the standard carb but have added slightly bigger jets and a spacer under the needle.

If you need a mikuni carb intended for a XR400R then i know where tehre is a new one at a very reasonable price  ;-)

GrahamH