I have a 1985 Evinrude 120 V4. It has been recently rebuilt. Since I purchased it, the lower starboard cylinder never fired properly. I performed a compression test with my daughter before buying it, and performed it again. Both times, it is within specs. 135-140 all cylinders. I suspected bad carboration and fuel. The fuel has been completely cleaned with proper filters and I'm currently running 89 OCT. The VRO pump has been disconnected so I'm running 50-1 mix. <br /> The carboraters have been completely cleaned with no change in the cylinder. I have even installed more carboraters, with no change. I have also interchanged with another cylinder. <br /> The spark is hot and blue, it has a new power pack. I tested the coils, which are fine. I even interchanged coils to the bad cylinder, which still had no effect. <br /> A couple of weeks ago, the porcelain insulator on the inside of the spark plug was broken. It did not break off, but slid back and forth on the metal electrode. <br /> The cylinder seems to fire above 2000 RPMs. All the spark plugs look nice and clean and firing properly. I have even interchanged the spark plugs. <br /> What's going on? Is there some damage inside the engine? All answers appreciated.<br /> Thank you. 
