Just had my FFR serviced, and had the carb replaced for a new Weber. It has now developed a chronic misfire, with occasional (loud!) backfiring. The chap who serviced it has beenslow getting back to me. Any thoughts on whether the problem is likely to be incorrect installation/adjustment of the carb or wrongly set up ignition timing?

had this problem on Series 3 109 2.25 and turned out to be faulty condenser!!
Bill Kingston