1978 55h.p.johnson motor loses power after 30 min. from 5000rpm to 2000rpm changed plugs ran fine for about 1 hr than same thing. new plugs look tarnished any ideas. thanks
corny,<br /><br />You are losing a cylinder. My best guess would be a coil. When it drops rpm. remove each wire and find out which plug is not firing.<br /><br />Then you can switch coils to find out if that is the culprit.
