Tweet
I have a 1998 Yamaha 150 HP Saltwater Series S/N 664 X 50277 mounted on my Grady White 204 Overnighter. This is a 2 cycle, carbuereted V6.
Background: The boat has been used regularly this season - mostly on weekends and has been running well. I try not to leave too much ethanol gas in it between runs and use sta-bil ethanol fuel treatment regularly. Over July 4th weekend, the motor was running fine when on plane (mid RPM to top end) but began stalling during low speed operation when docking, maneuvering, etc. It would re-start easily and you could continue maneuvering at low speed by giving it a bit more throttle and "bumping" in and out of gear. At this point I made a mental note to replace the spark plugs since its been 2 seasons.
Next run was on vacation July 16th. I launched the boat, maneuvered away from the ramp and when I advanced the throttle to put the boat on plane it bogged down and would not plane. I was able to get it to the dock at our rental house. I pulled the spark plugs, cleaned and replaced them. The motor ran fine after cleaning the plugs, going on plane with no problem. The next day, I put 6 new spark plugs in. The low speed problems noted above continued for the next two days. Finally on July 20th after running the boat most of the day, I went to put the boat up on plane and it repeated the same symptom as July 16th. We maneuvered back to the dock and I pulled the spark plugs. All the new plugs looked normal, except for cylinder 6 (bottom left) this plug was completely clean. I began checking for spark by having my son crank the starter while holding the plug about 3/8" from one of the head bolts. The entire left bank has no spark. The entire right bank has good bright blue spark which jumps the 3/8" gap to the head bolt. I noticed some corrosion on the ground lead where it attaches to the CDI bracket. The other end of the wire runs to the bottom of the left head. I also noticed corrosion on the bolt and ground lead of the # 6 ignition coil. I detached and cleaned both the connection and mounting surface with sandpaper. This made no difference but probably needed to be done anyway.
The only unusual event I can recall on 7/20 was the low oil tank alarm sounding. I immediately stopped and added two gallons of oil to the tank and all seemed well until I lost spark.
Background: The boat has been used regularly this season - mostly on weekends and has been running well. I try not to leave too much ethanol gas in it between runs and use sta-bil ethanol fuel treatment regularly. Over July 4th weekend, the motor was running fine when on plane (mid RPM to top end) but began stalling during low speed operation when docking, maneuvering, etc. It would re-start easily and you could continue maneuvering at low speed by giving it a bit more throttle and "bumping" in and out of gear. At this point I made a mental note to replace the spark plugs since its been 2 seasons.
Next run was on vacation July 16th. I launched the boat, maneuvered away from the ramp and when I advanced the throttle to put the boat on plane it bogged down and would not plane. I was able to get it to the dock at our rental house. I pulled the spark plugs, cleaned and replaced them. The motor ran fine after cleaning the plugs, going on plane with no problem. The next day, I put 6 new spark plugs in. The low speed problems noted above continued for the next two days. Finally on July 20th after running the boat most of the day, I went to put the boat up on plane and it repeated the same symptom as July 16th. We maneuvered back to the dock and I pulled the spark plugs. All the new plugs looked normal, except for cylinder 6 (bottom left) this plug was completely clean. I began checking for spark by having my son crank the starter while holding the plug about 3/8" from one of the head bolts. The entire left bank has no spark. The entire right bank has good bright blue spark which jumps the 3/8" gap to the head bolt. I noticed some corrosion on the ground lead where it attaches to the CDI bracket. The other end of the wire runs to the bottom of the left head. I also noticed corrosion on the bolt and ground lead of the # 6 ignition coil. I detached and cleaned both the connection and mounting surface with sandpaper. This made no difference but probably needed to be done anyway.
The only unusual event I can recall on 7/20 was the low oil tank alarm sounding. I immediately stopped and added two gallons of oil to the tank and all seemed well until I lost spark.