Honda CB1 NC27 5,000RPM misfire

[garth]

Hi

I have acquired a cb1 that won't play ball.

It runs well in any gear up to 5,000rpm and then misses.

It will still miss in neutral.

It previously ran well.

I've read about the 112mph restriction and the cdi going into limp mode etc - does anyone know which wires would cause these symptoms and which I should test?

Thanks
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You ain't a has been if you never was

[P.]

Speedo the original? On the CB400SF the restriction was in there, fitting a 2k resistor would bypass it, however I cannot recall the wire which controls this.

[wr6133]

If it's kicking in to the failsafe then somebody has probably already tried to remove it and fucked up, Look at the clock wiring and CDI wiring for badly bodged/cut wires. If that all looks normal then you need to get inside the clocks and see if some clown has tried altering the bit in the speedo.

Once you locate prior owners fuck up here is how to do it properly

https://hondacb400.myfreeforum.org/sutra122.php

[Scootaloo]

My first CB-1 started having trouble revving correctly when my electrics was about to die... shortly afterwards my battery exploded... I would charge the battery fully first and see if it makes a difference.
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(CBF125 - 09) (CBF125 - 11) (CB-1 - 89) (CBF500 - 06) (Push Bike) (CB-1 - 90) (XL125 - 01) (VF500 - 83) (GPZ500 - 94) (GPZ500 - 95) (GPZ500 - 87) (XV535 - 94) (XV535 - 94) (GPZ500 - 87)

[Scootaloo]

Good post above, following that link I found:

Just remove the fuse for (its 1 fuse mine is a 10Amp);
"meter, tail light, horn, turn, stop light, neutral light, hazard".

Then ride the bike, carefully!
remembering you have no indicators, no rear lights, no neutral light, no horn.

It should misfire at 5500 RPM, and believe me its noticeable.
If it doesn't misfire your bike has been derestricted already.

Sounds similar!
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(CBF125 - 09) (CBF125 - 11) (CB-1 - 89) (CBF500 - 06) (Push Bike) (CB-1 - 90) (XL125 - 01) (VF500 - 83) (GPZ500 - 94) (GPZ500 - 95) (GPZ500 - 87) (XV535 - 94) (XV535 - 94) (GPZ500 - 87)

[garth]

Not bothered by the restriction. Couldn't care if it is!

The clocks are original. Look untampered with.

How do I remove the trip knob to get the speedo face out?

I've found the 'restriction' wiring, as the above guide, but surely there must be a fault elsewhere if it ran ok previously?
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You ain't a has been if you never was

[garth]

oh, battery is new and lights work.
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You ain't a has been if you never was

[Scootaloo]

[garth]

Electrics don't just go bang by themselves

It's charging and everything else works, aside cutting out above 5k.
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You ain't a has been if you never was

[P.]

I'd still be looking towards the restriction.

5k is nowhere near it coming into its "power" if you can call it that, its rather fishy being close to that rpm killer restrictor of death.

[garth]

Will it shit itself if I join the wires without a resistor?
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You ain't a has been if you never was

[Scootaloo]

[P.]

[garth]

From reading more, it looks like if there is any disruption of those two wires it will cause the 5k issue.

Before i mess about with resistors i'll check for breaks in the wires.
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You ain't a has been if you never was

[garth]

Right then. There's continuity between the orange and blue wire at the clocks to the cdi - so no breaks there.

I'll try a resistor next.
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You ain't a has been if you never was

[map]

From left field I did come across this about power loss at 5k. Diagnosed as rotted exhaust.
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...and the whirlwind is in the thorn trees, it's hard for thee to kick against the pricks...
Gibbs, what did Duckie look like when he was younger?

[RhynoCZ]

Can you rev it up to the top at neutral?
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[garth]

[RhynoCZ]

[P.]

The restriction kills 2 cylinders and fucks up just after 5k, that is likely what the problem is. Not water in the carb.

[garth]

Picking up the resistor in the morning, forgot to check the 12v feed for the restriction circuit though. Could be that.
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You ain't a has been if you never was

[RhynoCZ]

[P.]

[garth]

I've done the resistor mod at the wires that go to the speedo.

Didn't fix it.

Bang on 5k every time, but runs so sweet other than that. Just about to get a strobe on the HT leads.
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You ain't a has been if you never was

[garth]

It would appear that cylinders 3 and 4 have an intermittent spark (on a closed throttle it dissapears?!)

WTF is that about.
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You ain't a has been if you never was