I have a 1998 4.3 Mercruiser that I just put new flappers in the exhaust after hydrolocking. I put new plugs and distributor cap on at the same time. Fired up and runs smooth, idles fine. I ran it at about 2000 rpm with no problem, opened it up and ran it about 3200 rpm. Temperature was 160 the entire time, oil pressure was 50 lbs. Within a minute or so it started pinging ( strange ping, not like backfiring through the carb) I dropped the throttle back to 1200 and it ran fine but everytime I tried to give it more throttle and it would do the same thing. I let it set idling for a few minutes and then gave it throttle and it ran fine. Hit full throttle and again the same thing. Slow down and idle and again the same thing. I only found one of the old flappers when I replaced them. I put a bore scope in and it looks like there is one at the bottom of the Y pipe, I tried a magnet and a 1/4 " rod with the end sharpened, I could get ahold but it wouldn't budge, and I wasn't sure it was a screen made into the Y pipe. My thought is if something is blocking the water from getting out and is building up back into the exhaust ports it. Is this possible or likely? I appreciate the help. Sorry so long, just trying to give as many details as I can.
