Originally Posted by Stooks

Hi guys, so I've replaced the sparks, the one by the rad just looked old but the one under the tank had black tar stuff all around the thread and the bit where it sparks. I changed both for new ones and it started beautifully at first, then it started to misfire. I took out the spark under the tank and it had a little more of this tar stuff but not as much as the original spark.what would cause this chamber to do this? Once again thanks.