Superfour misfire around 5,500rpm?

[craigs23]

Hi all

Wondered whether anyone can help.

I'm at a loss as to what's causing a miss fire on my bike. Doesn't matter if it's in neutral or in any gear, but as soon as the bike reaches 5,500rpm, it miss fires a bit.

It sounds a little like a rev-limiter kind of noise - very constant. It'll clear up around 6.5 / 7 k and then pull to the redline. The bike is extremely smooth revving up to this point with no hint of a fault.

My thoughts were it was electrical related as it's so constant, doesn't matter where I'm riding, how much throttle, etc, it always does it.

The carbs are spotless (ultra sonically cleaned), all the rubbers and gaskets are in tact, I've balanced the carbs, set the mixtures. The bike's had new coils, HT leads, spark plugs, air filter, oil and filter change, etc. Battery holds its charge, it starts on the button with no throttle even after a week of no use and idles very smoothly. Rectifier is working okay too. The bike has got CB1 clocks on, if this could make any difference?

Just running out of ideas for what it can be?

The bike has had a spill on the left hand side as the left hand side engine casing has a few marks on it. The wire from the pulse generator is putting out a decent flow as well.

Any ideas?

[craigs23]

I've been reading up on the old forum and found that it could be the old speedo restrictor problem - which makes sense as the bike's wearing US clocks....will be checking today, fingers crossed.

[craigs23]

Awesome, I have my 400 working as it should now.

Just spliced a resistor between the orange/blue wire and into the black/brown (12v mains) wire inside the headlight - problem sorted. My giant killer returns.

[meno]

glad its sorted have fun!

[zul_cbr]

may i know the resistor ohms ?

[Cammo]

You don't technically need a resistor (this is a kickback from vfr400 looms, which are entirely different and do need one - nc29, nc31, and nc35 looms are very similar and don't need a resistor).

Just join a wire between the orange/blue cdi wire and an ignition-on positive (easily found with a multimeter).

[zul_cbr]

You don't technically need a resistor (this is a kickback from vfr400 looms, which are entirely different and do need one - nc29, nc31, and nc35 looms are very similar and don't need a resistor).

Just join a wire between the orange/blue cdi wire and an ignition-on positive (easily found with a multimeter).

why they (29,31 and 35) dont need a resistor ? whats the ignition-on positive wire does ?

thanks

[Cammo]

You don't technically need a resistor (this is a kickback from vfr400 looms, which are entirely different and do need one - nc29, nc31, and nc35 looms are very similar and don't need a resistor).

Just join a wire between the orange/blue cdi wire and an ignition-on positive (easily found with a multimeter).

why they (29,31 and 35) dont need a resistor ?

I don't know why. The nc23 and nc30 DO need a resistor, but they have very different cdi's. The NC31/35/29 DO NOT need a resistor.

whats the ignition-on positive wire does ?

You can hook a wire straight up from a junction into the orange/blue cdi wire to the battery positive (+ve) terminal to get around the 180 km/h speed limiter.

[zul_cbr]

Thanks DataRacer for the info.

btw, my 29 using a resistor-mod trick and it works fine. my friends 23 and 30 also using the resistor-mod. i think, its better to play safe.

[Saash30]

Hi. I know this thread very very old but I have exactly same problem on my cb400 c31. And Im not English native. Could anyone explain a little easily how to eliminate this problem?
Best regards,
Aleks