nc24 tach reading wrong, any suggestions?

[CMSMJ1]

I reckon that your CDi is not telling the tacho right, or the tacho is a non NC24 one..

NEO will be the man - being the '24 guru par excellence...

As far as I can figure - the bike has 1 or 2 sensors - pulse generators - that tell the CDI when it needs to spark.

Obvously yours are working or you wouldnot have 4 cylinders..

I suspect something where either the CDI is not getting the timing pulses and so cannot tell the tacho the revs or that the tacho expects to get twice the pulses as it is not from an NC24... I reckon you have an NC30 tacho.

revs in top - normally are bang on 1000rpm = 10mph so at 70 mph on the motorway you would be around 7-8k revs. If yours is 3-4 then we have an idea of what is what!

don't think any dicking about would cause it, just a basic language issue between CDI and tacho

[suzbug]

mine is showing an engine speed of maybe 10-11k at 60-70mph, so its displaying high..
I will get the right figures tonight as i ride home, but to me it seems as if the tacho is getting too many pulses or displaying maybe double what it should.
Just to note, it does return to zero when the engine is off so the needle doesnt show an ofset or anything..

It looks like an nc24 tacho, the nc30 has the info lights for the indicators and such built into it in a different way..
unless somebody had gone to the hasssle of replacing the internals just to make it not work properly?? odd..

[Neosophist]

Hmmmm...

I can't remember if the tacho is driven off the negative from the coil or from the igntion box.

Do you have any pictures of the tacho unit?

I'm suspecting somethign is amiss here.

The NC24 only has two coils and uses wasted spark.. if it's getting its information from the coils and it's a 30 tacho it'll read double the amount as the NC24 has 4 coils not two.

Connect your NC21 tacho up and see what that reads. :) cut the plug off if need too and just shove the wires in, cant see you using the tacho for anything else.

btw it doesn't matter that the actual 'red line' on the tacho is drawn slightly lower than on the NC24 with your 21 tacho.. the Igntion box controls the red-line not the tacho.

plus it'll look 'cool' when your rev limiter kicks in and your tachos well in the red :)



btw thats what an NC24 tacho looks like.

Somebody could has also re-wired things but we'll look at one thing at a time..

[suzbug]

hi CMSMJ1, i just read your reply agian..

What you are saying makes sense because the nc30 needs two pulses, one per pair of cylinders, so if i had an nc30 tacho it would be displaying half what it should because there would only be one pulse per bang as it were....

but i think mine is diplaying in the region of twice as many as it should... so where or how can it get double the pulses??


confused...

[suzbug]

neo i bow to your knowledge!

yes, thats exactly what mine looks like! okay mine isnt as clean and shinny looking but it is the same.

you dont hapen to know which wires do what do you??

[Neosophist]

not off the top of my head.

3 wires?

power / earth / tacho signal?

have a look at the nc21 wire colours, they shouldn't be too far different?

[suzbug]

Hi guys. Just got home and I can Definatley tell you the tacho was reading 13k Rpm at 60mph (ish) in top gear!
I gave it some beans and the needle goes through the red and off the clock as the engine perks up! Didn't hit any rev limiter but the needle was Definatley trying to bend round the stop pin..

So, it Definatley looks Like it is displaying double the engine speed...

[Neosophist]

Yep.

Uncommon one that, not come across it before on the 24.

Trace the wire back from the tacho into the loom and see if you can see any obvious signs of it being messed about with.

If not i'd try the NC21 tacho next and see how you get on with that.

If that fixes it, safe to say your tacho is goosed and you can just get a new 24 one.

[karl BKK]

Could you possibly have the wrong tacho for the CDi you have, or vice versa?
My bike (vfr nc30) has an RVF tacho and has never read the revs correctly, but to be honest it doesn't bother me, as you/I/we shouldn't be looking at a tacho if you're carrying enough speed to be concerned about when to change gear :D
But of course it would be nice to have every thing working the way it should be :)

[suzbug]

i havent had chance to tinker with the bike yet, have been out on it enjoying the fun!
will try get the sanners out this weekend and have a play..

i will keep you all informed

Thanks
Suzbug