Sigma 1200 BC Speedo Problems

[ferguscawley]

I recently installed a new Sigma 1200 speedo on my GS as I no longer have a speedo drive with my new front (cast) wheel.

The first thing that struck me was that the cable from the 'base' unit that sits on the handlebars to the wheel sensor was way too short, so I spliced in some telephone cable to extend it by 18" or so. Good soldered joints and well insulated afterwards so no problems there (I assume).
I have programmed the unit correctly for wheel diameter/circumference etc but the speed being displayed is totally erratic.
The sensor is mounted securely to the fork leg, and the magnet is attached to a disc bolt via a strip of stainless steel. I will take some photos of the install later to show you how it is mounted.
The magnet I used is quite strong (taken from the top of one of those things with a flexible shaft that picks up lost screws/washers etc), is epoxied in place and is within 5 mm of the sensor when the wheel rotates.
Yesterday it showed that my max speed was over 200 mph (not bad for an 1100 ). The main thing that troubles me is how erratic the displayed speed is. It can jump from 25mph to 112 and back to 80 in a couple of seconds. It never does seem to display the correct speed.

Anyone got any ideas on how to sort this out ?.

Ferg

 

[richie]

Hi Fergus, As no one else has replied here is my 2p worth. I have used numerous bike speedos on pushbikes. The most reliable and easiest to use are cateye cordless but of course won't work on the bike due to electrical interference.

All cable speedos that I have used suffer much more from the alignment problems. When it says 1 or 2mm between the magnet and the sesnor it means exactly that. Even on a pushbike at 20MPH it makes a difference. Assuming that your extension is not the cause try and make sure the alignment and spacing between the two aformentioned parts is spot on.

Good luck

 

[ferguscawley]

Richie

Will experiment some more this evening. Thanks for your suggestions. As I said earlier, I will post a few pics of how I installed it when I get home this evening.

All the best
Ferg

 

[Padge]

You'd better watch out for that speed trap they have on the left on the road in from Blarney then..
You try explaining you were doing somewhere between 25 and 200 whenyou're pulled by Five-O..

Quick one.. How far down do you have the magnet on the wheel?
I had one on the last bike and put it really low (as near to the axel as possible). Brings the linear speed of the magnet passing the sensor as low as possible.
Not sure why it reads high though..