I have no spark on cyls 2 & 4. Spark is fine on cyls 1 & 3. Motor will start on muffs and sounds like its running OK. In the water it has no power and will only go very slowly. When I change the sensors, the spark moves to cyls 2 & 4 and none on 1 & 3. After doing a search on the forums, i believe this to be either a timing base problem or a power pack problem. The manual says to test with a neon test light - cant find one. How can I tell which part to replace - the timing base or the power pack. These are both relatively expensive and I would like to not guess wrong for $200 +/1 bucks.