cbr400, where would restriction be other than carbs?

Question

cleaned carbs and took out restriction shims but shes still topping out at 8000 revs. Any ideas?

Answer 1

On some Japanese bikes it's a small contact switch inside the rev counter, just disable this and it'll be fine. Ignore the self-righteous replies, a CBR400 needs its full rev range.

Answer 2

Are the throttle slides and cables adjusted so that they open all the way? Also remember that if you are going to go over factory rpm's and modify you will have to use larger jets in the carbs. Otherwise the increased airflow will starve the engine for fuel at high rpms. Jets are incredibly easy to change in most bike carbs and even the slides are usually adjustable as well. Manuals show all this in the carb section. Also if this is a "points and condenser" equipped bike points can actually "float open" at high rpms and cause the motor to not go past a certain point. A better quality set of points or adjusting the point "spring" can often clear that problem up. Back in the days when almost everything was points and condensers you could easily buy different quality points that had different prices accordingly. Valve adjustment is another angle as the valves can actually float as well, or simply be not opening up enough. Other than that and the other suggestions that others have posted the engine might require racing cams or some other "performance" enhancements.

Answer 3

Have a close look at the throttle linkage where the cable is attached to the carbs. On some restrictor kits there is a kind of tab washer which stops the butterflys opening fully. Ditch it.
I cant see it being electronic although it may be likely if it was factory fitted restrictor, its not something Ive heard of before.
From the sounds of the shims in the inlets, its an aftermarket kit and not that complex.

80 quid for 4 plastic washers and a bit of monkey metal!

They're having a larf!

Answer 4

Check the airbox inlet pipe needs to be quite a bit bigger than carb throats. Blocked aircleaner can cause loss of power at high revs.
Will it run to 8000 plus in first, if not check the ignition, failing to advance will restrict revs, whilst 8000 rpm should need less than 1/4 throttle.

Answer 5

I have had two Honda 400's, and you will almost certainly find some sort of restriction in the exhaust. Change it for something with a nice note to it.

I know my VFR400K (NC-21) had a sensor for top gear, that retarded the ignition curve, giving only a max 45bhp or top speed at x mph (long time ago you see). I have an NC-24 motor waiting in the garage still to go in.

But I digress....call West Coast Motorcycles, near Southport somewhere, who specialise in these imported bikes, and they will tell you straight off how to get it going right again.

And they do go well....

Answer 6

Hiya
I had an early one (the tri-arm version) and recall a red light above the speedo which was supposed to come on at around 120kph which is about 70mph and prevent you going faster!!
I unplugged it as it never seemed to do anything and to be honest the bike would redline in any gear and indicate 130mph (not on the road of course officer / people who want us to go under 70mph - asif that's gonna happen eh???).
To be honest your best bet is speaking to someone at Seastar Superbikes in Norfolk or BAT motorcycles who I think are in London - they are both huge in the grey import busines and will know the answer for sure!!!!
www.seastarsuperbikes.co.uk
www.batmotorcycles.co.uk

Hope this helps get you sorted, the cbr400rr is superb wish I hadn't sold mine :-(
Steve

Answer 7

More likely it is an electronic restrictor on a honda which is usually located somewhere behind the headlight if i remember rightly. There, by the way is nothing illegal about removing this, if of course you have the necessary licence? Don't think you'd find many pics of a cbr in a hot rod magazine though lol

Answer 8

electronic restrictor most likely.check for exhaust restriction aswell but that would just make it run like sh1t.

(Thomas D) Must be a yank to come up with such a stupid answer,
Its a motorbike ya flid!!!

Also there is nothing illegal about modifying a bike (cbr 400 should rev to about 12,000+ rpm anyway) so get a life danny.

Answer 9

i own a rvf 400, the cbr 400 is the same (a grey import).these were restricted in japan to 112mph.this was done by restricting the ignition timing and also the ignition box (do not confuse the reg/rec with this they are comp. diff.)haynes do a workshop manual this should help.also uprate your headlamps mine are crap yours are worse than crap.this should help your need for speed they are a good bike as are all 400s.

Answer 10

some restrictor kits have restrictor washers in the inlet ports and spacers on top of the throttle slides to prevent them opening fully, if the restriction is japanese home market it is normally a magnetic switch in the speedo, disconnect the cable and see if it still does it.