Thorspark Electronic Ignition advice.

[dennis.t]

I have posted here recently about my 1955 VH500 and problems with starting. After a frustrating couple of weeks fettling the carb with no success I have purchased a Thorspark electronic ignition system in the hope that I can eliminated the magneto as the source of the problem. This may seem an extreme measure but it may be worth a try. The bike fires most times on the kickstart but will simply not run.
Has anyone used the Thorspark system and if so what are the good and bad points?
Many thanks,
Dennis

[SteveShone]

Got em on a 1949 Matchless 500 and a 61 Panther M120 - they work fine. Accurate setting per the instructions can be a faff needing a timing disc/strobe set-up but to be honest I simply relied on the felt tip mark on the pick up they came with. It seems close enough and can always be tweaked on the advance retard lever These old engines are only one step away from a steam engine and generally not too fussy
Some folk will point to the need for reliance on a battery as a drawback. I've never found it to be even with a dead dynamo. The units draw very little current as the coil is only charged momentarily when the sensor is activated by the magnetic rotor - unlike a points system wherer the coil is being charged for the full cycle when the points are closed. I understand that they'll run happily on classic race bikes on a pack of AA batteries! A 6ah 6v battery will give days worth of riding and carrying a spare battery in the toolbox isnt that much of a drag just in case.
One thing that I have found important is that the battery needs earthing to the frame with a thick wire. Otherwise you can get a burst of small sparks at the plug rather than one big one.
I found that starting was easier and tickover more reliable than a fading mag - a lot cheaper too and much quicker than waiting for a mag to be overhauled.

Steve

PS I assume youve already tried a different plug - quality seems very variable nowadays even when buying from trusted sources

[paul.jameson]

Have the engine plates (the magneto platform one in particular) been repainted? If so, the magneto may not have a good earth, in which case run a wire from the terminal on the points end of the magneto to something like a cylinder base stud.

[dennis.t]

Steve and Paul many thanks for replying. Good advice about the battery earth lead. I have tried two spark plugs from different sources and the magneto is earthed to an engine bolt. Looking forward to setting up the Thorspark system. I have a strobe I used before to set up a Pazon system on my Norton so I am not entirely unfamiliar with electronic ignition.
Dennis

[robjameson]

When I fitted the Thorspark to my square four, I kept blowing fuses. The cause of this was the rear of the alloy plate that carries the hall sensor was arcing on the armature as it spun. I ended up having to fillet out a decent amount of material from the back plate to stop this from happening. It’s definitely worth taking your time with the fitting to iron out issues like this.

[dennis.t]

Rob,
Thanks for the advice. I am still waiting for my Thorspark to arrive. For my clarification was it the plate supplied with the sensor that had to be re-worked? And would I be able to check for shorting out using a meter testing for continuity i.e. an electrical contact between the armature and the sensor mounting plate when the armature is rotated by hand through the kick start with the valve lifter in use?
Dennis

[john.davies]

Hi Dennis, I fitted a Thorspark kit to my 1946 Square 4 a couple of years ago after the mag started playing up. What a difference it made, easy starting and running lovely. Perhaps Rob was a bit unlucky as my pickup plate fitted straight in with no fettling. The other good thing is that the Thorspark system keeps the manual advance/retard so setting up the timing is fairly straight forward. Use the mark on the pickup as a guide to get her running and then you can fine tune using the the advance/retard lever.

[dennis.t]

John,
It is good to know that you had a positive experience with a Thorspark set up. I'll check for arcing on the spindle but hopefully that won't be a problem.
Dennis

[robjameson]

Rob,
Thanks for the advice. I am still waiting for my Thorspark to arrive. For my clarification was it the plate supplied with the sensor that had to be re-worked? And would I be able to check for shorting out using a meter testing for continuity i.e. an electrical contact between the armature and the sensor mounting plate when the armature is rotated by hand through the kick start with the valve lifter in use?
Dennis

Yes, it was the back plate which the hall sensor is mounted to. You can check with a multimeter quite easily.

[dennis.t]

Rob,
Thanks for your reply.
I received my Thorspark on Monday and fitted it yesterday with no real problems. Most of the time was taken up routing the wiring. The spark is good and actually much better than the magneto spark. However, after a violent backfire on my first attempt at starting the VH500 I decided to sleep on it and go back another day. The bike was timed accurately on the magneto so I was hoping that fitting the Thorspark might work without re-timing being necessary. Unfortunately it was not that simple. My bike seems very sensitive to timing adjustments and simply aligning the felt tip pen mark on the sensor with the magnet on the rotor was not effective, partly I suspect because the magnet is about 3mm wide so any alignment with the felt tip pen mark is necessarily approximate. I have to fall back on trial and error rotating the magnet back or forwards in small increments. Thorspark recommend final adjustments using a strobe light, which I have, but what is the reference timing mark?
I time the bike at 5/8" before TDC so not much use timing with a strobe and I do not want to take the primary chain case off to use a timing disc.
Dennis