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I just got done installing a new to me 750 double pumper carburetor on my 1990 7.4L 454 engine in my boat. The guy I got it from is supposedly a marine mechanic, stated to me that it had just ten hours of run time on it. I put brand new plugs in it & started it, it was pretty hard to start. After running it for approximately ten minutes, I shut it off and pulled the plugs and this is what they looked like, black soot. Any suggestions? I did adjust all four idle mixture screws out the 1 1/2 turns.
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