Dodgy ignition coil??

[NJA]

I've got a little Stihl kombi unit that suddenly cut in use.  I presumed fuel so filled it up, but noticed still probably ¼ of a tank in there.  It then wouldnt start.

Checked spark, nothing doing. 

Put new spark plug on, still nothing

 

Put a tester on the spark plug lead, shows a spark when earthed to the machine, but not when connected to a spark plug.

 

Even with a plug i took off a working saw or a new plug (had been in workshop for 5years but still in box)

Maybe all 3 plugs are mysteriously duff but Im beginning to doubt it?

Disconnecting on/off switch doesnt make any difference so can't be that

 

Could it be that the ignition coil has gone a bit dodgy, works when tested on its own but not when connected to a plug?  Almost as if the resistance of the plug is too much?

 

Just want to check I'm not doing something stupid before ordering a new coil.

 

Thanks

[Mark_Skyland]

If you remove all the wires going to the coil and you're sure that the HT lead isn't shorting out and you have no spark at the plug then its usually the coil that needs replacing. 

 

[spudulike]

Double check the coil to flywheel gap and if you can unscrew the HT lead ( some you can), then unscrew it, check the continuity, clean it and refit it.

It is also worth checking the continuity between the HT cap and earth. You should get a reading of sorts, possibly 20k ohms, but it will show the cap and lead are OK before purchasing a coil.

I had a 461 once that had a corroded HT line and this check saved purchasing a new coil.