Hi, I'm looking for help diagnosing a problem on this 1981 120 Mercruiser with the Chev 4 cylinder engine. It will run fine all day long cruising at slow speeds about 1500 rpm but after any runs at planing speeds it develops a miss on #2 cylinder. After a few minutes of slow speed operation the dead cylinder picks up again and it runs fine. It doesn't make any unusual noises while it's doing this.<br /><br />This boat is new to me so I don't know how long it's had the problem, or the repair history. Here's what I did to the engine after I bought it - new plugs, coil, replaced points with pertronix electronic ignition, replaced worn distributor with good used one, adjusted timing, carb, & choke to specs.<br /><br />To try and locate the problem I've pulled the pertronix and put the points back in, and I've replaced the #2 plug wire after it starts missing. Neither made any difference. I can't think of anything else in the ignition that would act this way. Now I'm considering the possibility that one of the valves is set too tight and the lifter pumps up enough at high rpm to hold the valve open, then adjusts back down after some time at low speed operation. Any thoughts before I pull the valve cover? Any other ideas?<br /><br />Thanks,<br />Joe
