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40 HP Mercury runs rough at low RPM's
#7446521
04/23/12 01:02 PM
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Joined: Sep 2009
Posts: 654
Bug-e
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Pro Angler
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OP
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Posts: 654 |
I have a small aluminum bass boat with a 40 HP Mercury (1999 model motor). The motor runs great over about 2500 RPM, but when running at low RPM while trailering, idling, etc., it runs very rough and frequently stalls. I'm a newbie with outboards (had the boat for a year), but it almost seems like a carb or idling adjustment to me (total guess on my part). Are there common causes for this? Plugs were replaced and carb "rebuilt" (carb kit installed?) last spring right before I bought the boat.
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Re: 40 HP Mercury runs rough at low RPM's
[Re: Bug-e]
#7446535
04/23/12 01:04 PM
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Joined: May 2003
Posts: 11,586
gary purdy
TFF Guru
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TFF Guru
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The world will not be destroyed by those who do evil, but by those who watch them without doing anything. Remember what He has done and remember that He is not done yet!-- GOD IS GOOD
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Re: 40 HP Mercury runs rough at low RPM's
[Re: gary purdy]
#7446595
04/23/12 01:29 PM
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Joined: Sep 2009
Posts: 654
Bug-e
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Maybe. I probably haven't burned through a whole tank of gas this spring. But maybe I will take the boat out on the lake and make sure I burn a whole fresh tank. I fish smaller lakes (Gibbons Creek, Bastrop), so it's definitely true that the engine doesn't run much on most of my trips.
Last edited by Bug-e; 04/23/12 01:32 PM.
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Re: 40 HP Mercury runs rough at low RPM's
[Re: Bug-e]
#7447306
04/23/12 04:48 PM
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Joined: Sep 2009
Posts: 654
Bug-e
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Any other common issues I should investigate?
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Re: 40 HP Mercury runs rough at low RPM's
[Re: gary purdy]
#7553506
05/21/12 04:16 PM
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Joined: Sep 2009
Posts: 654
Bug-e
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I think Gary was right. Burned through two tanks of gas on Caddo and now the motor has never run better.
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Re: 40 HP Mercury runs rough at low RPM's
[Re: Bug-e]
#7556397
05/22/12 03:45 AM
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Joined: Dec 2005
Posts: 4,058
Gungle
TFF Team Angler
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TFF Team Angler
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Not only is it old fuel, but the old fuel has varnished you carb over the winter. Will it run better at low rpm with the choke on? You're going to need another carb rebuild. Be sure to treat your fuel before you put it away for the winter.
Cheers,
George
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Re: 40 HP Mercury runs rough at low RPM's
[Re: Gungle]
#7558562
05/22/12 07:10 PM
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Joined: Sep 2009
Posts: 654
Bug-e
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Not only is it old fuel, but the old fuel has varnished you carb over the winter. Will it run better at low rpm with the choke on? You're going to need another carb rebuild. Be sure to treat your fuel before you put it away for the winter.
Cheers,
George It did run better at low rpm with the choke on, but after running a tank of fresh gas the engine runs smooth at all rpm's. Hopefully there wasn't significant varnish buildup. I will definitely be more careful in the future to avoid this problem. I do use Stabil on a regular basis.
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Re: 40 HP Mercury runs rough at low RPM's
[Re: Bug-e]
#7561076
05/23/12 03:30 AM
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Joined: May 2012
Posts: 81
Amy Saterfiel
Outdoorsman
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Outdoorsman
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thumbs up
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