S/Rocket fitted with Lucas Rita AB11. Was running fine until last week. Has just started misfiring with no power over 1/8 throttle and blue flames from pipes. Removed 389 carb and stripped. All clean, no water in bowl, with minimal wear. Refitted, fuel flow checked ok and engine fired up on 2nd kick. Warmed up on fast idle then increased the revs. Again no power over 1/8 throttle (approx. 2500-3000 rpm) and started backfiring with blue flames from the exhaust. Changed spark plugs, still the same. Has anyone had a similar experience or a solution. Rita not the best electronic ign. system, starting to suspect the amplifier box auto adv/retard breaking down. Mistral Eng. of Chigwell, Essex did an upgrade for the amplifier box (MOIRA) but apparantley ceased trading several years ago. Can anyone recommend other experts on this system. Thanks...