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Power to HT lead but no spark


sherco2702
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Hi,

Hopefully someone can help, bike is a sherco 250 2004 (leonelli ignition). Had a couple of issues with it previously not starting when hot, typical problems that point towards the stator going caput. However out running a few weeks ago and it was ticking over fine after running for few hours then it just slowly starts to die and cuts out. Since then I've not managed to make it run again. Checked everything I can think off, looking at previous forums etc etc. Carb has been stripped several times, thats clean, put a bigger pilot jet in to a 36 instead of 32 which is supposed to ease the starting. Tried several different new plugs, no joy. Sent stator away to Steve at Motoplat, had the typical issue as all the others apparently and was repaired. Checked all earthing and thats good, the only thing I haven't tried is putting a new CDI unit on. I can't find any previous forums or advise that anyone has had issues before with the CDI's, only the stators.

If you put an inline spark plug bulb on the bike and kick it off it faintly lights, so faintly you need to have the garage lights off to see it light. But it will not produce a spark.

Losing the will to keep investigating and reluctant to spend £130 on a new CDI if its not going to fix it.

Any help greatly appreciated as its getting the weather to get out there!!

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It has happened that the CDI box on this model has failed. This is not common but does sometimes happen. You will have to decide if spending the money on a part that may not be faulty is worth the gamble.

 

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Ignition coil may have a defective primary or secondary winding, in other words a broken wire. Hence your stated ‘power to ht lead but no spark’. The engine running for a while and then stopping is indicative of the coil wire being broken internally. Double check the coil earthing to frame before removing. Also easily missed, but have you changed/checked the spark plug cap? The CDI unit as the name states contains the capacitor which may have gone open circuit. Can you borrow (rather than buy) from another bike the suspect parts to eliminate before spending out?

Are you using a multi meter to check electrical items etc. Ignition coil should have a range of between 0.5 to 3 ohms between wiring connector tabs on coil body. From neg terminal to ht lead 7+ thousand ohms, you will need exact specs from w/shop manual. £130 for a CDI unit sounds a lot, most are not repairable unless you burn out the resinous sealing and can get at the pcb and find the faulty component. The time and frustration in doing this plus possible health issue due to burning the resinous sealant out needs to be taken into account. Maybe another CDI unit from a breakers might be worth considering. 

Bet after this little lot you find it to be something simple and obvious, but then we have all been there at some stage or other, good luck.

Oh, I don’t recommend sticking your CDI unit in the oven either, not good for other half relations or the CDI unit. You might try a hot air gun to warm the body of the unit but I doubt it will have any effect. If moisture has got in the unit the damage will have been done.??

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36 minutes ago, section swept said:

Ignition coil may have a defective primary or secondary winding, in other words a broken wire. Hence your stated ‘power to ht lead but no spark’. The engine running for a while and then stopping is indicative of the coil wire being broken internally. Double check the coil earthing to frame before removing. Also easily missed, but have you changed/checked the spark plug cap? The CDI unit as the name states contains the capacitor which may have gone open circuit. Can you borrow (rather than buy) from another bike the suspect parts to eliminate before spending out?

Are you using a multi meter to check electrical items etc. Ignition coil should have a range of between 0.5 to 3 ohms between wiring connector tabs on coil body. From neg terminal to ht lead 7+ thousand ohms, you will need exact specs from w/shop manual. £130 for a CDI unit sounds a lot, most are not repairable unless you burn out the resinous sealing and can get at the pcb and find the faulty component. The time and frustration in doing this plus possible health issue due to burning the resinous sealant out needs to be taken into account. Maybe another CDI unit from a breakers might be worth considering. 

Bet after this little lot you find it to be something simple and obvious, but then we have all been there at some stage or other, good luck.

Oh, I don’t recommend sticking your CDI unit in the oven either, not good for other half relations or the CDI unit. You might try a hot air gun to warm the body of the unit but I doubt it will have any effect. If moisture has got in the unit the damage will have been done.??

By ignition coil do you mean the CDI or the stator? I've tried several different plug caps so cant be that.

Unfortunaly not that year of bike, my friends got a 2003 but it uses the ducati ignition so its a no go there. Looks like i'm going to have to just buy a new one CDI i think. It has had a new one in the past. The guy i bought it off gave me the old one but i cant remeber why he said he had changed it.

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You’ll hate this, CDI sends a much faster and powerful charge to the ignition coil. The CDI unit is triggered by the Hall effect sensor or trigger as some call it (little black or grey unit close to crankshaft where the points would have been on older engines) this is the component that electronically sees the timing/ignition point. The Hall sender/sensor can work quite well even when its starting to break down in performance. Did you send the Hall sender to be checked at the same time as the stator. I’ve replaced no end of these senders, they can perform just like a human with toothache, it’s hurting like hell but there’s no sign of pain when the dentists approaches??I bet the previous owner went through the same checks you are now involved with. Hall senders can become unstable in that one moment they work and then the next nothing. Many ignition systems get pruned down in design so that the coil sits directly on top of the spark plug and there is no HT lead just a cap to connect to the plug, again one coil per plug produces more efficient ignition. What was wrong with the stator? Hope you sort the problem out, please keep us posted?Your CDI unit may contain the Ignition coil, on some systems it’s a separate item. Testing the ignition coil is the same procedure as for seperate coil, but you need to know the electrical specs for your particular unit. 

Edited by section swept
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Quite possible for it to be the HT lead, 1 of the times I thought I had a dying stator it turned out to be a crack shorting directly to the head.

My ignition is the same type & age

Have you talked to the guys at splatshop, they'll be able to give you things to check 

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  • 2 months later...

Just an update for you all. Turned out to be the CDI breaking down as described by section swept. Bought a new one and it fired first time. Must have not been able to generate the 000's volts it required to make a spark. Getting the stator rewound must have also helped because the throttle response now is so much better, its not always  trying to stall when you are going very slow in gear. thanks for the help!

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