Help please CB400 2002 6th gear not revving properly

[Biker au]

Hi,

I just bought a bike yesterday, 2002 Japanese import Honda CB400 superfour. Riding in gears 1-5 is fine but when in 6th gear the bike is jerky and loses revs, has anyone come across this issue before and can you recommend what it may be? Need to work out if it needs fixing urgently or if I can still ride it in the lower gears as only need 6th on the highway.

Any help/ advice would be much appreciated,

Thanks

[_mjs_]

Have you checked for restrictors?
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Previous Bikes: 2006 Honda XR125L > 2003 Yamaha DT125R > 1996 Honda CB500
Current bikes: 1997 Kawasaki ZZR 600 E5 > 2006 Honda Varadero XL125V

[Biker au]

No I haven't, had would I know if it has a restrictor on it or has a fault? In 5th revs to redline and go fast but in 6th won't rev at all and stutters

[Taught2BCauti...]

Bikes made for the Japanese market could be fitted with a Speed Limiter!

See this article - https://hondacb400.myfreeforum.org/sutra122.php
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Honda Varadero XL125(V8)
www.TheFutureIsHere.eu

[Biker au]

Thanks, issue as it was happneing at 110kph not 180 so had to ride in 5th with the revs high, wouldn't allow any kind if accelerating in 6th

[Taught2BCauti...]

A speed limiter of some sort is the only explanation for your problem that I can think of.

If your bike does have one, and I think there's a good chance it does, it might not be working properly - causing the problem to occur at a different road speed.
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Honda Varadero XL125(V8)
www.TheFutureIsHere.eu

[Biker au]

Thanks, so no mechanical issue that would have those symptoms? Hopefully it is a restrictor that can just be removed, will take it into a garage for an inspection

[DOS]

I believe the restriction is in the clocks.
If you could get a loan of clocks and try them out.

In the mean time you could go up one tooth on the front sprocket and down two one back sprocket and just use 5 gears.

[Vincent]

+1, speed restrictor is electronic and on the speedo pcb

There may be some more details and pics on the Grey Bike Forum.
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Space Is Deep

[Teflon-Mike]

If its an electronic speed-limiter, it'll retard the ignition at whatever speed its set to, regardless of rpm's.

6th gear will be an over-tall ratio or 'over-drive' to knock the revs back for more relaxed cruising, and in all liklihood, on a bike with only 40bhp or so, all stacked at higher rpm's it IS likely to go 'faster' in 5th, where lower ratio will let you rev to where peak power is made.

Think about it; 40bhp, will just about get you to about 110mph on a good day, but to do it you'll need the motor spinning pretty much bang-on peak-power revs, what, 12,000? But to hold 70mph only needs about 12-15bhp, which you probably have from anywhere above 3,000rpm. If 'top' gear was geared to deliver 110mph at 12,000 revs, then 70 would fall at 7,500rpm, and would still be rather 'buzzy'. So putting a taller gear over 'top', an'over-drive', could drop the revs at 70 back to perhaps, 5,000, just before it starts to get 'busy'... but that would imply nearly 170mph at peak power.... but, with only 40bhp, you are never going to be able to do 170.

But, this is why bikes like this with peakpower made with a lot of rpm's will have six-speed gearboxes, not five, and you will need to use the lower gears more to get at that high rpm power, so stirr the box, so to speak. Something that can be rather alien if you have come from a DAS bike with a broad flexible power delivery; slightly less so if you have come from a 125, that with limited power can need the gears worked a lot to get at what they have, but which tend to have 'top' matched pretty closely to best speed their power can pull, without an 'over-drive', as they don't have any excess power to hold 'higher-speeds' with less revs.

Or short.... COULD just be the 'nature' of the bike...a small displacement, high-reving multi, and absolutely nothing to do with power or speed restrictions... its just a rev-happy bike.
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[Kickstart]

Hi

Another vote for a Japanese market speed limiter.

The odd thing is that it cuts in at ~110kmh. The 180kmh limit is 112mph which is a remarkably similar number. Wonder if someone has tried to fit and screwed up some kind of speedo healer.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Biker au]

Thanks everyone, really appreciate the advice. I am concerned I've bought a turkey that will need a transmission rebuild, fingers crossed its a japanese limiter that can be removed without too much troubles. I'll just ride in 1-5 for now, until I take it in to get checked out.

[Biker au]

One strange thing though to suggest it is not a limiter is that it goes above that speed in 5th gear up to 120-130kph just can't hold revs in 6th, so would suggest it's something associated with that gear instead of just top speed, or if the limiter is only active is 6th perhaps?

[Teflon-Mike]

[Taught2BCauti...]

Found this on the website I mentioned in my first post, referring to OP's model:

[Vincent]

Found the original speed restrictor thread, it does seem odd that the restrictor would operate in 6th and not 5th tho

https://hondacb400.myfreeforum.org/Japanese_Grey_imports_400cc_180KMPH_RESTRICTOR_about5.htmlNampus
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Space Is Deep

[GeorgeB.]

on My CB, 6th gear is only good for crusing at around 90ish. It wouldn't really pull. 5th is where all the power is, managed around 120 before bottling it in 5th.
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Current: '99 Fazer 600 | '99 Range Rover P38 4.6 HSE
Previous: Keeway TX125 | CBF 125 | CB400SF Project Big One
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[Kickstart]

[Major Doss]

Have a look in this month's Practical Sportsbike, they have a feature on derestricting the restriction in the restrictive speedo.

tl;dr E Gads, Tef man! You do waffle some utterly useless bollocks, sometimes! keep it up.

[wr6133]

If it is similar to the one Kawasaki used on the ZZR400 then bypassing it is fairly easy. It's a photosensitive thingy in the speedo and a wire to the CDI. You can either try shaving down the bit in the speedo or just put a resistor in the wire to the CDI.

[cb1rocket]

Does it not hold any speed in 6th? Or is it clunky? Sounds like transmission has gone to me.

I own a cb1 and yes the speedo limiter kicks in at 180kph, easily bypassed. Feeding a live into the sensor will disable it
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Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

[Biker au]

It would hold the speed but when attempting to accelerate loses revs instead of gaining them and fails as if something is not right, can't be how the bike is supposed to behave surely. Would that be a transmission problem? All other gears work fine bike pulls well and changing gear is not a problem just 6th

[wr6133]

[tarlowb]

Biker au! ('')

I have this exact bike, exact year and unfortunately...exact problem.

Have you found a solution to this? I presume you either fixed it, or sold it/scrapped it! there has been no action on the post for over two years. I have narrowed it down to either a problem with the JDM restrictor, or transmission failure.

obviously its going to cost a bomb to rebuild a transmission and I don't want to start off down that route if its not necessary.

I am looking under the clocks this weekend to investigate, but a few days ago I replaced the headlight bulb. hoping I've just knocked something out of place as it was fine before!

lovely bike when it works ('')

any help would be insanely appreciated!

[tarlowb]