Check the STOP wire is not shorted - sometines switch mounted on the engine brake develops a short. If that's not it, you will need a new coil, which is easier said than done. Spares for these engines are just about unobtainable new - except for service items.
I have used Tecumseh coils in the past - suitably re-drilled to suit the mounting holes on the SV150 engine. I can supply a NEW modified coil for £25.
phil_saunders(a)bigfoot.com
Phil Saunders
April 2010
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