I recently replaced my QuadraJet four barrel carburetor on my 1990 Sea Ray Sundancer boat. I replaced it with a 750 double pumper carburetor that had supposedly 10 hours on it approximately. I put it on the engine and for some reason it's extremely hard to get it started, but once I have it running it seems to run great, quick throttle response and everything. But one thing I do notice is I check my spark plugs and they have a black sooty substance on them. Not oily, but like it’s carbon, the engine is new. Any suggestions?