The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: eugenius on 31.03. 2024 12:26
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Hi friends, here I am again with a neverending journey about my reassembled A10 engine. Resolved the issue of the carburator screw now facing with a spark plug failure: no spark from one of the new spark plugs. The bike starts good but only one cylinder is working. Tried to see the spark activating the starting pedal with dismounted sparks plug and only the left one makes the spark; tried to clean or invert the spurk caps, clean the electric cables. Nothing. May I ask you an advice? Ciao, Eugenio
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Soft/bad quality pick up brushes. They leave a carbon trace on the slipring thus diverting both sparks to one plug.
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The Lucas K2F magneto uses one set of contact points to produces the sparks, which are then fed to the cylinders alternately, by the slip ring on the armature. In other words the plugs do not fire together, as on some other ignition systems.
So the fact that the bike runs on one cylinder means the spark generating part of the system is working, and the fault is in the distribution of the spark. Suspect the slip ring, and then the pick up/brush, plug lead, cap and spark plug of the dead cylinder. A mechanical fault on this cylinder is also a possible, but for now try this.
Inspect the magneto slip ring and pick up carbon brushes. They all need to be clean, brushes are spring loaded and move freely. Morris is on the money here.
Still no better? Change the plugs over. If the fault also changes sides, it's the plug. If the good cylinder still runs, the plugs are OK. Similarly swap the leads and plug caps. If the result is that the poor cylinder still won't fire, then suspect the pick up and its brush, plug lead and cap. The old trick of holding the plug lead close to the cylinder head with the engine running lets you see a spark jump on the dead cylinder if all is in order. Hold the lead with a piece of wood or insulated pliers or wedge between the fins. A good spark from the end of the lead and it still won't fire the plug indicates a plug, plug cap or mechanical problem.
Swarfy.
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Thanks all for the precious advices. I'll try the sequence and I'll be back to you. Eugenio
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Yes. If it turns out to be a lead unscrew the plug cap and check the screw is contacting the copper, its possible to screw the cap into the insulation and have no connection.
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Thanks limeyrob! That's also something to check better. I'll do it. Eugenio
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you dont mention what plugs you have ....I have had the best luck on my super rocket with Champion N4 C lots of problems using NGK plugs .
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Thanks Sean, actually I have bought two new NGK B8ES and following several tests yesterday night it seems that one of the new plugs is not working properly! No spark from one of the new plugs. Is it possible? Inverting the plugs the sparks on the left cylinder seems normal. Ciao
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sorry, on the right cylinder that was the failing one *smile*
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Thanks Sean, actually I have bought two new NGK B8ES and following several tests yesterday night it seems that one of the new plugs is not working properly! No spark from one of the new plugs. Is it possible? Inverting the plugs the sparks on the left cylinder seems normal. Ciao
there are lots of fake NGK chinese copies on the market if you go on NGK web site they show you how to identify them ....and yes you can get a dud plug in any brand but its rare these days .
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There are indeed so many fake NGK plugs now I have gone to using denso instead
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If you are still running an older vehicle with conventional plugs and leads, where access to the leads is easy, put your suspect plug into a convenient lead, rest the plug on the engine and start up. Sure, one cylinder will be dead, but you will have a quick visual show of the plug working. Maybe not recommended for catalytic convertors etc, but it sure solved a mystery non start on a Honda Mower......with a NGK BR8ES long reach plug. FAILED!
Swarfy.
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Brisk plugs are good. Apparently they will take being cleaned unlike most other modern plugs. Not cheap but highly recommended especially if your old clunker is a bit of an oil burner..
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thanks all. So maybe better a Champion N4C or a Brisk?
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or even a good, genuine NGK BE8S plug to match your OK one!?
I've heard of problems with NGK but I've never found this myself having settled on B8ES running standard unleaded fuel. Also NGK are mainstream and available in most markets, Champion less so if 'stralia is anything to go by.
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or even a good, genuine NGK BE8S plug to match your OK one!?
I've heard of problems with NGK but I've never found this myself having settled on B8ES running standard unleaded fuel. Also NGK are mainstream and available in most markets, Champion less so if 'stralia is anything to go by.
try small engine shops for Champion used a lot in lawn equipt etc
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or even a good, genuine NGK BE8S plug to match your OK one!?
I've heard of problems with NGK but I've never found this myself having settled on B8ES running standard unleaded fuel. Also NGK are mainstream and available in most markets, Champion less so if 'stralia is anything to go by.
try small engine shops for Champion used a lot in lawn equipt etc
At the mower shop we only use NGK's and have always myself. Very rare to get a dud. Back in the "day" I used Champs and had more trouble with them!
Cheers