1989 Mercruiser 454 magnum (rectangular port heads)
all stock, quadrajet carb, aluminum high-rise intake
Pushes a 1989 baja sunsport 210 (21') with a 25p turbo prop
Recently changed intake manifold gaskets due to small leak. Took it out to lake for first time and it ran flawlessly, intake leak definitely fixed and engine running great.
Then about 5 hours into the day (probably 1.5 hours of run time on boat) while trying to pull tubers I got a loud clatter on takeoff. Idled home after that with a tick the whole way. It ticks at idle and gets worse as rpms go up. Here is a video so you can hear the ticking noise.
Anyways, I also found that the #8 spark plug is black as can be (dry, carbon black, not oily). All other plugs on that side are a decent tan color (about what they should be at idle). FYI, the oil level is fine (not losing any, not low) and the engine temp is in normal operating range, nothing close to overheating all day (highest temp probably 170 degrees).
Am I looking at trouble with a valve??