Ahoy. We have a 2 stroke 8 HP 2009 8MSH. We inherited this engine when we bought a sailboat in 2020. It had been neglected for some time before we bought it and we have no information about it's prior history. We don't use the outboard very often; it often sits on the stern rail for several months between uses.
For the first couple of years, it would run great and could easily get the dinghy planing with 2 people aboard, but only if we changed the fuel pump diaphragms before each use. Without new diaphragms it would bog down and stall when it was in gear and throttled above a slow crawl. To keep it running, we had to play with the choke to control speed instead of the throttle. Even if we only ran the engine once for 10 or 20 minutes, the next time we opened it up the fuel pump diaphragms would be all distended and wrinkly.
We took it to a Yamaha mechanic who suggested changing the carburetor. So I bought an aftermarket carb on eBay and installed it. I also went through the maintenance procedure to set the length of the timing and throttle cables. Now it starts easy and runs well every time. But the throttle tops out at something like 50%. Turning the throttle up further sometimes causes a slight decrease in speed. I've checked the jets (even swapped them with the ones from the old carburetor) and replaced the fuel filter. Measuring the resistances of the ignition module gave readings that don't match the maintenance manual I have, but a spark tester on the ignition cables shows spark at both plugs.
Any suggestions what to try next? It's definitely an improvement to have an engine that runs every time without a new fuel pump. But planing was fun and we miss that.
Thanks in advance.
For the first couple of years, it would run great and could easily get the dinghy planing with 2 people aboard, but only if we changed the fuel pump diaphragms before each use. Without new diaphragms it would bog down and stall when it was in gear and throttled above a slow crawl. To keep it running, we had to play with the choke to control speed instead of the throttle. Even if we only ran the engine once for 10 or 20 minutes, the next time we opened it up the fuel pump diaphragms would be all distended and wrinkly.
We took it to a Yamaha mechanic who suggested changing the carburetor. So I bought an aftermarket carb on eBay and installed it. I also went through the maintenance procedure to set the length of the timing and throttle cables. Now it starts easy and runs well every time. But the throttle tops out at something like 50%. Turning the throttle up further sometimes causes a slight decrease in speed. I've checked the jets (even swapped them with the ones from the old carburetor) and replaced the fuel filter. Measuring the resistances of the ignition module gave readings that don't match the maintenance manual I have, but a spark tester on the ignition cables shows spark at both plugs.
Any suggestions what to try next? It's definitely an improvement to have an engine that runs every time without a new fuel pump. But planing was fun and we miss that.
Thanks in advance.
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