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Old 07-04-2019, 13:48   #1
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Mercury 6hp Two Stoke Issue

Hello all,

I picked up a used 1996 Mercury 6hp outboard. When I went to look at it, I was told it was running great. Took a long drive to get to it and turns out it had an issue. The idle primer bracket was broken. I was able to start the motor by actuating the choke and idle throttle with my fingers. Now I have replaced the bracket, and when I start the engine with the choke out the RPM's go WAY too high.

After I push the choke in, I get some smokey "backfiring?" that nearly stalls the engine.

I can't get the engine to ever run at a low idle as it eventually stalls out.

Any ideas what could be going on?
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Old 07-04-2019, 16:51   #2
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Re: Mercury 6hp Two Stoke Issue

Hopefully, you're starting the motor in water so you don't burn the impeller. The throttle either isn't closed all the way or there's an air leak, usually the carb gasket. There should be a spring on the throttle plate shaft that holds the throttle closed at idle. Linkage could be holding it open. Air leak can also be a vacuum hose missing.
As with all 2 cycle outboards it's probably from sitting. If it was run or stored with gas including ethanol, there could be internal carb damage from an acid that forms from the ethanol. Also today's gas is unstable and always need a conditioner if stored. Varnish can form on the internal parts, blocking ports or just restricting them enough for the engine to run bad. Thank the EPA.
You should be able to find gaskets and a rebuild kit. There are aftermarket carbs, sometimes on ebay.

I have a Merc outboard as wall art to remind me never to buy another. I use an electric now, much less trouble.
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Old 07-04-2019, 17:43   #3
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Re: Mercury 6hp Two Stoke Issue

Iím with Lepke on this one. But I would reset the mixture screw to zero and back it off, I think it is 1.5 turns from memory, but check online. Who knows what has been done to the mix to try to get it to run in the past.
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Old 08-04-2019, 04:03   #4
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Re: Mercury 6hp Two Stoke Issue

Quote:
Originally Posted by Lepke View Post
Hopefully, you're starting the motor in water so you don't burn the impeller. The throttle either isn't closed all the way or there's an air leak, usually the carb gasket. There should be a spring on the throttle plate shaft that holds the throttle closed at idle. Linkage could be holding it open. Air leak can also be a vacuum hose missing.
As with all 2 cycle outboards it's probably from sitting. If it was run or stored with gas including ethanol, there could be internal carb damage from an acid that forms from the ethanol. Also today's gas is unstable and always need a conditioner if stored. Varnish can form on the internal parts, blocking ports or just restricting them enough for the engine to run bad. Thank the EPA.
You should be able to find gaskets and a rebuild kit. There are aftermarket carbs, sometimes on ebay.

I have a Merc outboard as wall art to remind me never to buy another. I use an electric now, much less trouble.
Hi, thank you for the info.

Yes running it in a bucket. The water pump seems to be working fine.

The screw you are talking about, is it #36 in the diagram?

When I pull the choke out, is the throttle also supposed to increase? As it is assembled right now, when the choke is open, the idle throttle is as open as it can go. When I push it in, the throttle goes down a bit.

I suspect it was stored for a while with gas in it.
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Old 19-04-2019, 05:36   #5
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Re: Mercury 6hp Two Stoke Issue

Hello,

So I got a gasket kit and cleaned out the carburetor. It starts easy now, but it still revs high on start and idles high. And I get smokey backfiring (watch 20 seconds into this video):

https://photos.app.goo.gl/htdt7VkM1kjWka5T8

Also, I'm not sure where the mix adjustment screw is? Would it be here?
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Old 19-04-2019, 15:36   #6
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Re: Mercury 6hp Two Stoke Issue

Yes, that looks like it. Turn if fully clockwise then back it off 1.5 to 2 turns as a starting point.
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Old 19-04-2019, 15:38   #7
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Re: Mercury 6hp Two Stoke Issue

Also check that the fast idle knob has been rotated fully anticlockwise and pull it then push it back in fully a few times to make sure it is returning itself fully, they do stick a bit.
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Old 19-04-2019, 15:53   #8
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Mercury 6hp Two Stoke Issue

Quote:
Originally Posted by svenskflicka View Post
The screw you are talking about, is it #36 in the diagram?


When I pull the choke out, is the throttle also supposed to increase? As it is assembled right now, when the choke is open, the idle throttle is as open as it can go. When I push it in, the throttle goes down a bit.
No, screw #43.


Yes, the behaviour you describe with the choke is what happens on my engine (8 hp merc, same series as yours, looks just the same except mine is a LOT more scruffy)
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Old 19-04-2019, 15:58   #9
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Re: Mercury 6hp Two Stoke Issue

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Originally Posted by GILow View Post
Also check that the fast idle knob has been rotated fully anticlockwise and pull it then push it back in fully a few times to make sure it is returning itself fully, they do stick a bit.
Thanks, yea it is sticking, how do I unstick it?
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Old 19-04-2019, 16:27   #10
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Re: Mercury 6hp Two Stoke Issue

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Thanks, yea it is sticking, how do I unstick it?
Where is it sticking?

If itís the plastic plunger, maybe silicone spray? Can you take a video of the sticking problem?
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Old 19-04-2019, 16:43   #11
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Re: Mercury 6hp Two Stoke Issue

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Where is it sticking?

If itís the plastic plunger, maybe silicone spray? Can you take a video of the sticking problem?
Seems like the left arm is binding. I'll take a video tomorrow. Thanks for the help!
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Old 19-04-2019, 21:50   #12
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Re: Mercury 6hp Two Stoke Issue

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Seems like the left arm is binding. I'll take a video tomorrow. Thanks for the help!
It is a pretty clunky mechanism... I'll try to have a look at how mine behaves, but not sure when I will get time to get to the boat.
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Old 21-04-2019, 17:59   #13
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Re: Mercury 6hp Two Stoke Issue

Well, she is running a LOT better now. But she is making this ticking sound, like a spark plug, and it sometimes stops and then the engine runs perfect (watch 30 seconds or so into the video)

https://photos.app.goo.gl/ASfq7peaSycTEwc76

Thoughts?
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Old 21-04-2019, 23:00   #14
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Mercury 6hp Two Stoke Issue

Sounds like one of the HT leads is leaking. Easy to find, but NOT RECOMMENDED, by touching the leads while the engine is running. Once youíve been resuscitated youíll probably remember which lead it was.

Try running the engine in the dark, you should see the spark jumping from the leads, or the lead caps, to the block. Might be a simple case of cleaning the leads and caps.
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Old 21-04-2019, 23:02   #15
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Re: Mercury 6hp Two Stoke Issue

Also, how many turns of the idle mix screw did it need to reset the screw completely and how many turns did you back it off to get it running?

And one more thing, faulty HT leads seem to reveal themselves more often when the mix is lean, in my experience. No idea why, but Iíve seen it a lot over time.
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