Ignition

[smsxr05]

I was wondering if anyone out there has ever heard of the problem i have. I have just had my model 20 rebuilt with eletronic ignition added and im getting it ready for its MOT. I took it for a short spin up and down the lane just to get it warmed up (so i can torque the heads down again later). When i turned the ignition off the bike kept running !!!??? although the engine did sound slightly different with the key ON than it did OFF. I have checked the ignition switch and wiring with a meter and all seems correct (i'm a qualified sparky by the way) I have heard of diesel engines with this problem i.e. running on their own lub oil but never a petrol engine. Any ideas on what may be causing it?

[Groily]

Weird or what!? You don't say what sort of electronic ignition unit you've got. If it's one of those modern 'BTH' independent spark generators I suppose it could be independently spark generating over-enthusiastically. Presumably it's just an earth that stops them by shorting out the low tension side, although I don't know. But if it's a normal Boyer Bransden type thing, it is surely consuming some current (I assume you've got a working ammeter?) to make it run after the engine is 'stopped' unless you have so much incandescent carbon in there that it runs on indefinitely.
Have you tried disconnecting the battery to see whether it stops then? If it doesn't, could the thing somehow have been wired so that the dynamo feeds it directly (although at tick-over one would expect it to stop as the cut-out, be it mechanical or solid state, should open and isolate the dynamo).
Be interested to hear what the problem is when you find out!

[CR]

Need a lot more info - like dynamo or alternator, what electronic unit fitted and how you've wired in the feed to the ignition control (box)? The most likely cause would be that you've inadvertently selected a live feed from an original ignition switch that has both IGN and EMG connections, i.e. when the engine is running it's providing a direct feed to the switch for emergency starting as well as a feed from the battery via the ammeter.

As a test, simply provide a switched feed to the electronic ignition directly from the battery (fused of course) and by-pass any existing switched circuits. If that works you should be able to work your way back through the main switch connections with your meter...

If you're using a Boyer power box (I'm assuming you're running 12 volts) then you can dispense with much of the original switch wiring. The emergency starting is provided via the capacitor in the power box.

If this doesn't help, more detail is required...

[smsxr05]

Bill / Chris,
Thanks for your input. A little more info as requested.

The engine has just been completly rebuilt, rebore pistons etc. The ignition unit is a 12v "Classic Solutions" model and it is wired with a feed from the battery to the new ignition switch and then direct to the control box. I have checked the switch and it works fine. I will be firing it up again one night this week with a meter connected and will turn it off as soon as it has settled down to tick over. If it still keeps running that indicates to me that it may be electrical but if it does turn off then i'm wondering if the ignition timing or something else is out and produces this effect once the engine is hot. Again i will check the timing before i let it run for any lenght of time. I have also just purchased a "Colortune" to check that the carb is working as it should. Forgot to say that its dynamo. Steve.Edited by - smsxr05 on 02 Sep 2008 2:38:56 PM

[Duncan]

Steve, I had a similar problem when I changed an oil soaked magneto for a distributor on my G12.

I had non standard wiring with the ignition switch isolating the battery from the circuit which I assumed would stop the current to the coil, however when the battery was isolated the engine would continue to tick over but if you open the throttle it would die, I can only surmise that the power some how back feeds (you may have guessed by now that I am not an electrician) while the engine is still generating it. My solution was to place the ignition switch on the feed to the coil although a double isolated pole switch would also do to totally isolate the battery.

The bike was running an alternator at the time but I can not recall if it was fitted with a black box or traditional rectifier at the time.

You may be asking a lot of your dynamo to run 12v and electronic ignition if you intend to use the lights much, Lawrence has some experience in this field (pun intended).

[lawrence]

quote:
Lawrence has some experience in this field (pun intended).


I hope you have kept the magneto Steve

[smsxr05]

All,
Its all my fault, i have learnt 2 lessons....Just because it looks right doesnt mean it is right and never trust someone elses wiring. The non standard wiring was very well done with lables and everything but, and its a big but the lables were wrong. It transpires that the dynamo was indead back feeding into the wiring loom and feeding the ingnition thus the engine would continue to run. They tell me that these electronic ignitions are very touchy as far as voltage is concerned so if i hadn't have had the dynamo uprated to 12v with new armature and coil but just changed the regulator then this problem may never have happened. Some times you do what you think is the right thing but it doesn't work out the way you planned. Anyway bike should be on the road later this month if all goes well with the MOT.
Thanks again to all who replied.
And no Lawrence i didn't keep the mag, i sold it to Rick.Edited by - smsxr05 on 03 Sep 2008 11:22:55 AM

[Groily]

Well done! Had to be a rational explanation and very glad you got to it so fast. Probably right about the sensitivity of these things - but have to say I haven't had the urge to change over from magnetos on my bikes.
Happy riding - assuming the MOT goes as per plan . . . I'm sure you'll love it because they are great machines.