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Post by hawker63 on Jul 30, 2023 9:56:55 GMT -5
2007 Regal Commodore. Our boat has 2x8.1l Mercury inboards, gas. 2 fuel tanks, both over 1/2 full. Engines can pull from either tank but I think they tend to pull primarily from tank on the same side as engine.p. Both filled same day so same gas. About 3 weeks ago, port engine starts tp run rough on startup, sounds like knocking for first 15 min so I can run at 1500-2000 rom, but regardless of throttle position it won’t go above this speed. Starboard engine fine. After 15-20 min, I can accelerate board. Port still seems to hunt a bit on rpm, but after 30 min, problem goes away. New plugs and wire were done when we bought boat in 2020 so I don’t think it’s that.
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Post by sgilbert on Jul 30, 2023 12:51:43 GMT -5
First thing I would do is buy 2 cans of Seafoam or Techtron & put in each tank. Run the snot out of them and then decide if you need to go further.
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Zane
Full Member
Posts: 74
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Post by Zane on Jul 30, 2023 14:28:49 GMT -5
I'd do the same as sgilbert, assuming all filters are new. I'd do fuel and air filters. Not sure how many hours you put on your boat but I did plugs every year in my last boat. Also if you did plugs and wires did you do dist cap and rotor as well?
Spark, air or fuel, it's one of those..
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Post by hawker63 on Aug 20, 2023 14:28:31 GMT -5
We had marina work on it, replaced plugs and engine is smooth now. Plugs were done spring of 2020 and have about 80 hours on them. Marina didn’t keep to show me, I should probably do the starboard. Surprised they were the issue.
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Post by tc33obx on Aug 20, 2023 15:25:21 GMT -5
Just the plugs or did you replace the spark plug cables as well. Plugs could be the issue, but so could the cables or better yet a disconnected one or one that wasn't completely engaged. Maybe the boot was over the plug but the metal in the cable wasn't connected to the top of the plug. When any of my engines, cars or boat, start running rough quickly, I normaily start with the spark plug cables and make sure both ends of the cable are connected to the plug and the distributor or computer that drives the plug spark.
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Post by hawker63 on Aug 20, 2023 20:08:26 GMT -5
Great feedback. The wires were all replaced in 2020 when we bought the boat. I was thinking it was fuel filters or cool fuel module or water as problem went away after 20 minutes of slow speed. If it comes back, I’ll check wires and pull the plugs myself to check.
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