I have a Seca 550 (I think - not absolutely sure) that has troubles idling, apply some revs and it seems to run OK - but at idle (1100 rpm) it splutters and stalls. I have replaced coils and checked resistance on all wires from CDI. I have 2 theories - timing chain? or CDI unit? I stripped the carbs and cleaned and replaced rubber manifold inlets, carbs are in great shape and fuel flow is fine. Any ideas? Plug caps are new and plugs I think are OK and it cant be HT leads as they have all been replaced.