I replaced my distributor cap and rotor but I didn't use a marine rotor which is round and has fins in the bottom of it I used an automotive rotor. My engine was running fine the whole day and then it started backfiring when getting to the marina. I changed all my spark plugs again but it is still backfiring. I am thinking it is pick up coil sensor that maybe the marine rotor was designed to keep it cool or something. Is this part difficult to replace and will I need to remove the spindle and re adjust the timing?