johanwahlberg
Member
Hi,
got our first boat this summer, an 80's 16 ft hard top, just for trying out boat life. The enginge, 70hp Mariner, 2-stroke, 3-cyl from 1979, has worked fine except for a few occasions (of seemingly increasing frequency) where it has been running unstable below a certain rpm threshold. It starts fine at the first or second attempt, but runs with some "unstableness", when I slowly increase the throttle, I reach a pretty evident threshold where the unstable engine sound transform into a smooth, spinning, "healty engine" sound. My tachometer is disconnected, but I'd say its around approximately 20-25% throttle, which gives 10-12 knots of speed. After a while's running, returning to dock, and turning the throttle down below the rpm threshold, the engine usually start sounding even more unstable than in the beginning, when cold. This phenomenon has been more prominent the last 5-8 times we've been using the boat. At one point did i get a complete stall at almost idle rpm, when throwing the anchor at slow speed...
This video shows the engine and the sound just after returning to dock after a 45-min run. You can see the whole engine shake at the point of almost stalling: https://vimeo.com/141407456
Any ideas?
I'll bring the boat up for winter in a couple of weeks, and my intention was to do the regular maintenance such as change oil, impeller, etc. I was also thinking to try cleaning the carburators to see if that could be the problem. I'm pretty good with mechanics and electronics, but haven't done engines before...
Edit; It might actually be two separate problems because the almost-stalling-problem (seen in the video) is pretty new, but the unstable/uneven runing seen at low rpm's has been much longer.
Here is also a sound recording during acceleration with the transition between unstable - stable engine audible. Not the best recording but if you listen carefully you can hear the engine sound shift in character around 00:07-09, and 00:54-56. https://clyp.it/vc2wztgs
got our first boat this summer, an 80's 16 ft hard top, just for trying out boat life. The enginge, 70hp Mariner, 2-stroke, 3-cyl from 1979, has worked fine except for a few occasions (of seemingly increasing frequency) where it has been running unstable below a certain rpm threshold. It starts fine at the first or second attempt, but runs with some "unstableness", when I slowly increase the throttle, I reach a pretty evident threshold where the unstable engine sound transform into a smooth, spinning, "healty engine" sound. My tachometer is disconnected, but I'd say its around approximately 20-25% throttle, which gives 10-12 knots of speed. After a while's running, returning to dock, and turning the throttle down below the rpm threshold, the engine usually start sounding even more unstable than in the beginning, when cold. This phenomenon has been more prominent the last 5-8 times we've been using the boat. At one point did i get a complete stall at almost idle rpm, when throwing the anchor at slow speed...
This video shows the engine and the sound just after returning to dock after a 45-min run. You can see the whole engine shake at the point of almost stalling: https://vimeo.com/141407456
Any ideas?
I'll bring the boat up for winter in a couple of weeks, and my intention was to do the regular maintenance such as change oil, impeller, etc. I was also thinking to try cleaning the carburators to see if that could be the problem. I'm pretty good with mechanics and electronics, but haven't done engines before...
Edit; It might actually be two separate problems because the almost-stalling-problem (seen in the video) is pretty new, but the unstable/uneven runing seen at low rpm's has been much longer.
Here is also a sound recording during acceleration with the transition between unstable - stable engine audible. Not the best recording but if you listen carefully you can hear the engine sound shift in character around 00:07-09, and 00:54-56. https://clyp.it/vc2wztgs
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