Sounds odd...quick lead check - try pulling plug lead out of suspect cylinders and putting them near a ground point (stick a screwdriver in boot where plug head goes on and check for spark near a good ground by holding screwdriver shaft near (1-2mm) an engine bolt.) make sure theres no raw fuel/fumes around before you try tho.
Also, dont touch anything on body if you hold lead or screwdriver or you\'ll get a jolt lol - done this a few times - not a nice feeling!
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