Hi all,<br /><br />I have an '81 model merc 18hp two cylinder single carb. SN 59118844<br />Cruising along nicely and suddenly dropped revs.<br />Top cylinder runs fine. Have good spark, changed plugs, compression good - 145psi on both.<br /><br />With the motor running, I ground the lower HT lead - no change. Coils checked out ok. tested with test plug<br /><br />If I ground the upper HT lead the engine dies.<br /><br />Being a single carb and the top cylinder running fine, I don't think the carb is the problem. I am thinking maybe a broken or stuck open reed or blocked exhaust port.<br /><br />Am I on the right track? Just want to get some good advice before pulling things apart.<br /><br />Anything else I should check for?<br /><br />Cheers - FM