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Have a 2016 Yamaha 150 with 350 hours. My boat partner started noticing a slight shake or vibration the last time he used it. I took it out yesterday and felt a moderate shake under load and it is running rough all together. Its chattering at idle and when you accelerate it sounds gutless and like it is only running on 3 cylinders. It would only make 4400 RPMS under load but will make full rom in neutral. Here are the bullet points of what ive done so far to investigate.
-Pulled the spark plugs. 1-3 had black build up on the threads but the anode and cathode looked good. When I got to cylinder 4 the boot felt like it wasn't seated all the way. When i pulled 4 it was hammered and had black on the threads, insulator, anode and cathode. It almost appeared that there was oil on the threads as well. I went and got four new spark plugs and ran it again. Still only 4400 RPMS and shaking. The new plugs on 1-3 again had minor black carbon buildup and 4 looked like crap. Still had oil (or something similar) on the threads. I decided to clean off the new spark plugs thinking the boot from cylinder 4 was to blame but it still would only make 4400 RPM but all four of the spark plugs looked more consistent.
-Next I changed the fuel water separator and dumped the old one to look for water and found nothing.
- I ended up doing a compression test and all four cylinders were exactly the same around 148.
Im going to call the mechanic monday but with the long wait times I wanted to check here to see if you all could point me in the right direction.
-Pulled the spark plugs. 1-3 had black build up on the threads but the anode and cathode looked good. When I got to cylinder 4 the boot felt like it wasn't seated all the way. When i pulled 4 it was hammered and had black on the threads, insulator, anode and cathode. It almost appeared that there was oil on the threads as well. I went and got four new spark plugs and ran it again. Still only 4400 RPMS and shaking. The new plugs on 1-3 again had minor black carbon buildup and 4 looked like crap. Still had oil (or something similar) on the threads. I decided to clean off the new spark plugs thinking the boot from cylinder 4 was to blame but it still would only make 4400 RPM but all four of the spark plugs looked more consistent.
-Next I changed the fuel water separator and dumped the old one to look for water and found nothing.
- I ended up doing a compression test and all four cylinders were exactly the same around 148.
Im going to call the mechanic monday but with the long wait times I wanted to check here to see if you all could point me in the right direction.
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