Actually found some time today to try and locate a replacement coil a magnitron variant and after contacting B&S this is what they suugeested
The original coil is http://www.briggsandstrattonparts.co.uk/briggs-and-stratton-armature-magneto-298968
and the Magnitron Version they recommend is this http://www.briggsandstrattonparts.co.uk/briggs-and-stratton-armature-magneto-398811
Before I order it Has anyone fitted one of these? and are they difficult to set up?
The engine details are Model 170702, Type 5638-01, Code 80082211
Many thanks