My mercury 2 stroke only seems to be sparking on cylinders 1 and 4. the spark plugs on 2 and 3 seem to be dead. i have checked the spark plugs and HT leads on all 4 cylinders and they are ok. it has 4 seperate coils which i have yet to swap around. does anyone know of any obviuos solution to this problem or is it a case of just trial and error. any suggestions will be greatfully received. the engine is from the 70's i think with twin carbs. <br /> many thanks in advance.