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Merc 6hp dies above low speed even with clean carb. See Video.

T

theinteresthunter

New member
Below is a link to my video showing the problem in use and at sea - a real-world condition.

This motor is a 2016 4 stroke (with about 35hours of use). The motor acts pretty good right at the beginning. Then after 10mins to an hour, it will eventually die (like it’s not getting enough gas) when going higher than low speed (where the tiller is just twisted beyond “Restart”). I can prevent it from dying by quickly lowering the speed. Seems to be a problem only when in gear as it doesn’t die in neutral when I rev it up. When it dies, it will always start up with 1-2 pulls. I can always run at low speed with the throttle just beyond the “Restart” label. But any more than that and the problem repeats.

The problem seems to worsen with running time. Also the problem seems to be worse in wavy conditions.

I’ve used both external and internal tanks. I've changed out fuel lines, external fuel tanks, pump bulb. And this is maybe the 5th time cleaning the carburetor (which means completely disassembling, cleaning, putting it back together).

I’m having the exact same issue with my 2014 Merc 3.5 hp (not shown in the video). It also has about 30 hours of use on it.

Some people have suggested replacing the fuel pumps and the control modules. These motors are not too old and have low hours on them. But if I do, will I be replacing them with more poorly-made fuel pumps and control modules?

See the video:
 
Have you checked for spark when it stalls? before replacing untested parts troubleshoot her, Borrow a fuel pressure gauge from an auto parts store. Have you tried pumping primer bulb while she's running?
 
This may sound crazy, but I would go spend the $15 and get a spray of Mercury Powertune and use as directed...I just went through a miserable time with my 20hp 4 stroke....it was just all carboned up...see of that helps... Good Luck!
 
For a start that engine is far too low in the water which can cause condensation issues with the electronics. (Worse in wavy conditions?)

When she starts to die is there an improvement when the primer bulb is squeezed? If so fuel pump is suspect.
 
Milgrip said:
For a start that engine is far too low in the water which can cause condensation issues with the electronics. (Worse in wavy conditions?)

When she starts to die is there an improvement when the primer bulb is squeezed? If so fuel pump is suspect.
Click to expand...

I usually use this on a SoloSkiff with an external tank. When using the external tank, I have the same issues as when using the internal tank (as shown in the video). I've replaced my tank, fuel hose, and primer bulb, fuel filter, with brand new gear and have the same problem.

The water splashing on the motor is just during this video. Also, my brother and I were toward the back of the boat in order to make the video... making the boat stern heavy and creating a lot of splashing on the motor. The rest of the day there was minimal splashage due to proper weight balancing. This was the first time I've used the motor on this boat... but the problems aren't from just this one outing; these motor problems have been happening when used the SoloSkiff. So when I say "wavy" I literally mean wavy not as in "splashy". 100% guaranteed splashing is not the problem here as I will also have this problem on glassy calm water too... (both with this 6hp and my 3.5hp with the identical issue).

Another note: I always run Sta-bil 360 Marine fuel treatment and stabilizer.
 


Is the cavitationplate about the same height as, or up to two inches higher than, the keel / bottom of the transom with the motorin neutral trim. As you are having thesame problem with both engines I would check this out and aso the possibilityof using contaminated fuel.
When you remove the cowling is there any sign of dampness or condensation, the engine compartment should be completely dry. Have you removed the sparkplug and checked the colour to see if its fuel starvation or running too rich? Its a process of elimination. How old is the fuel you are using? Is there any sign of water/condensation in the fuel? The carb jets are so tiny, a minute speck of water in the float chamber can cause serious running problems.



 
Milgrip said:
Is the cavitationplate about the same height as, or up to two inches higher than, the keel / bottom of the transom with the motorin neutral trim. As you are having thesame problem with both engines I would check this out and aso the possibilityof using contaminated fuel.
When you remove the cowling is there any sign of dampness or condensation, the engine compartment should be completely dry. Have you removed the sparkplug and checked the colour to see if its fuel starvation or running too rich? Its a process of elimination. How old is the fuel you are using? Is there any sign of water/condensation in the fuel? The carb jets are so tiny, a minute speck of water in the float chamber can cause serious running problems.
Click to expand...

The cavitation plate location is good on both motors.

Both motors have been using new fuel and used at separate times and with different but new fuel. Every time I'm using Sta-bil. There's no dampness in the cowling when I take it off.

I don't know how to check for water/condensation in the fuel. Isn't there a water-separator in these motors?

I'm going to run some Seafoam in it and see if it helps today.

I keep suspecting the fuel pump if both my motors eventually seem to get starved from fuel at higher throttle under load.
 
I'm sorry for all the problems you're having with your mercury engines. Like Johnnygir said, if you pump the primer bulb right when it starts to slow down, and it speeds back up, then you'll know that fuel supply is the issue. It sure sounds like its running out of fuel.
 
Later this week, during calmer weather, I'll be testing again by pumping the primer bulb when it does seem to die. I'm pretty sure I tried that in the past. But I'll try it again. I may also spray starting fluid in the air intake when it starts to die.

I'm curious if you guys have ideas on what other issues it might be as well, that way I can brainstorm while I'm at sea this week. Thanks!
 
I took the boat out yesterday and distributed weight on the boat so the motor was about 6-8" higher than in the video. It ran pretty good for awhile but then, like all my past experiences with it, eventually had the same problem. I had an external tank this time so I could pump the primer bulb when it started to die. It did not help. It died about 8 times and each time I tried pumping the primer bulb. The primer bulb was not soft when I did go to pump it.

I didn't get a chance to spray starting fluid in the air intake because it was a hair to splashy where I was and at the higher speeds (for testing) and I didn't want to get saltwater on the exposed parts. I'll have to try that on another very calm day.

Any ideas?
 
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