Rev counter reading double

Right, the ratbike's had a makeover. I've cut the front subframe off,
put the headlights on the forks, rewired and added some new
blingdictaors and fitted the chrome[1] speedo and tacho.

Now, with a little faffing about and trial and error, I've got
everything working properly except the tacho, it's reading I guess
double what it should - This wouldn't be a problem as I could half the
revs but it only goes to 15,000 rpm and my bike redlines at 10,5000rpm.

Now, I wired it into the existing loom because I thought his would be
easier and save messing around taking the tank off to connect it to the
negative side of the coil. Thing is, is there or would there be
something in the Honda rev counter to make it read half what the new one
is and how do I connect it to the negative side of the coil? There's
four of them and there's no obvious negative side.

I'm going to try running a wire tomorrow just to see but it'd be helpful
if anyone could give me a clue as to what might be up and any remedy if
the wire running doesn't work.

Ta.

[1] This will soon change with the addition of some exhaust paint

 

In communiqué <>, Whinging

A quick Google suggests this is not an unknown problem when fitting a
tacho from a different bike. Some ignition systems use a 'wasted spark'
which could fool a tacho not designed for the bike or the number of
coils may be different hence too many pulses.

A relevant discussion which may shed light here:
http://www.yamaha-rd.com/forum/topic-34170.html

--

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| Pete Fisher at Home: |
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| Gilera GFR Moto Morini 2C/375 |
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Are you sure there are 4 coils IIRC there's only 2; one does cylinders 1
and 4, the other 2 and 3. The rev-counter is probably counting each pulse
as a firing stroke and I'm fairly certain that the fatblade has a 'wasted
spark' system where the plugs fire on the exhaust stroke as well.

How to fix it? **** knows. Is there anything you can set on the
rev-counter.

 

In uk.rec.motorcycles, Pete Fisher belched forth and ejected the
following:

A couple of things...

First, one bloke talks about a tweakable pot. I did notice a gromit type
bung in there and thought it was the bulb. I'll check that tomorrow.

Also, someone talking about a Mito saying when they used the HT wire it
read double but when they used another one it read true.

I don't know if there is another wire but as that was the first one I
tried and it appeared to work, that's the one I used.

I had to pack up in a hurry because it was getting dark but I'll have
another look tomorrow, cheers.

 

In uk.rec.motorcycles, Mups belched forth and ejected the following:

Yes, you're quite right. There's two

I'm not sure.

What I thought was a bulb might not be. There's a thing with a small
screwdriver sized hole in it. It could either be a bulb or a thing to
calibrate it.

 

Whinging Courier wrote

Pictures man, where are the fucking pictures?

 

In uk.rec.motorcycles, steve auvache belched forth and ejected the
following:

Patience man!

 

In uk.rec.motorcycles, steve auvache belched forth and ejected the
following:

You're an impatient ****.

Here's three..

Jesus...

http://i97.photobucket.com/albums/l220/whingingcourier/DSC00031.jpg
http://i97.photobucket.com/albums/l220/whingingcourier/DSC00030.jpg
http://i97.photobucket.com/albums/l220/whingingcourier/DSC00029.jpg

 

I fitted that setup to my GTRat. I hooked the pickup wire from the tacho on
to the original tacho feed in the loom. The unit I bought was for a twin, I
figured thats what I needed with the wasted spark ignition. Did you buy the
one for a four cylinder bike?, if so, the wasted spark ignition might be
the cause.

Must finish the rat. Need to attack the back end ( of the bike ) with an
angle grinder, though it does look kinda nice/sweet/shyte ( delete as
applicable ) with its luggage on and that front end.

 

In uk.rec.motorcycles, Moon Badger belched forth and ejected the
following:

That's what I've done.

I bought one "for a Honda".

I don't think there's any difference; the instructions say attach the
green wire to the negative side of the coil. There is no negative side,
just that pickup wire you mentioned.

Being able to put luggage on is a good thing.

You could always attack it and rebuild it to look completely different
but luggage friendly.