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Old 10-06-2024, 21:28   #1
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Question I have a 6HP outboard (Mercury) that dies at high revs...

It's a fairly new engine... 2-3 years old. Was working fine until my friend wanted to help and sprayed WD-40 ALL OVER the inside... he said it would protect against rust.

Now... it runs fine in NEUTRAL... even when I rev it REALLY HIGH in neutral... but when I put it in D, I can only do low revs... then it dies when I do high revs.

Any idea? What should I do? Can I try to fix it myself or send it to repair?

Thanks, guys!!
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Old 11-06-2024, 03:46   #2
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

No real clue, but you might try a different fuel line from the tank... in case the original is collapsing under vacuum or some such. In that case, maybe nothing to do with the WD-40 treatment.

Or try different fuel lines inside the housing, ditto the collapsing idea. Not sure if WD-40 could have caused something like that or not.

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Old 11-06-2024, 05:02   #3
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

Sounds like dirty jets in the carb to me. Probably worth taking the carb off, cleaning, and blasting out the jets with some more of that WD40. I doubt the WD40 was the cause of your problems unless possibly he shot a lot right down into the carb, but that should clear out pretty quickly after a minute of running the engine.
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Old 11-06-2024, 05:52   #4
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

When it dies, how does it behave? Does it stutter and cut in/out and then quit? Or does it just kinda go "flat" power-wise and then die if you continue to push it?
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Old 11-06-2024, 06:19   #5
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

Check the oil level.

A club mate was having a similar problem.
Yamaha outboard has a build-in safety feature which reduces RPM's when the oil pressure is too low.

Perhaps yours has the same feature.
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Old 11-06-2024, 06:44   #6
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

Sounds like stereotypical "not getting enough fuel". In neutral it doesn't need much fuel to achieve high revs, but in drive it does. Places to look are clogged carb, clogged fuel filter, clogged fuel line, tank vent not open, etc.
One test is to pump the priming bulb while it's running, if it doesn't help, it's likely carb.
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Old 11-06-2024, 07:08   #7
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

IMHO you're friend is misguided in what WD-40 is and what it does. It's not fogging oil. It's really a penetrant and water displacement. It serves as a decent cleaner. It is a fairly poor lubricant and is not really a replacement for machine oil. In decades, I've never seen anyone use it to oil a hunting rifle, for example.

In fact, over time, I find WD-40 cakes. Did he spray it into carb air intake? I definitely wouldn't blow out carb jets with WD-40.

See if the engine revs under load with the choke closed.

I agree this sounds like a fuel issue. My first step would be to clean the carb. If the engine has been using ethanol and is 6-8 years old, I'd just replace the carb. They are usually under $100. The carb rebuild kit ends up being 60+% of the cost of a new carb and comes with the mounting gasket.
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Old 11-06-2024, 07:12   #8
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

Ethanol in fuel will eat anything made out of plastic.
Check fuel lines, filters, etc, and see if you find anything unusual
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Old 11-06-2024, 07:38   #9
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

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I definitely wouldn't blow out carb jets with WD-40.
Maybe WD40 isn't ideal for it but I've used it for this many times. The thin red straw is perfect for sticking in there to blast out any crud. But, there are dedicated carb cleaners you can use too. In fact, there's a dedicated WD40 carb cleaner: https://www.petes-tools.com/can-you-...-a-carburetor/
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Old 11-06-2024, 11:53   #10
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

I agree it sounds like a carbon problem. Our mercury 8hp (2 stroke) would start and run ok but always lacked power especially at full revs. Had the carb cleaned and still no good. Put a new carb in and it has run perfectly ever since (touch wood ��).
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Old 11-06-2024, 13:11   #11
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

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Originally Posted by Kettlewell View Post
Maybe WD40 isn't ideal for it but I've used it for this many times. The thin red straw is perfect for sticking in there to blast out any crud. But, there are dedicated carb cleaners you can use too. In fact, there's a dedicated WD40 carb cleaner: https://www.petes-tools.com/can-you-...-a-carburetor/
I hear you. They also make carb cleaner in a aerosolized can with a red straw too. If I were stuck in some cove, sure.
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Old 11-06-2024, 13:45   #12
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

It's not the WD40. How long did/does it sit? Gas with ethanol will cause issues if not run often. I buy non ethanol gas for all yard and outboard use now. It's a huge difference.
A few years ago my brand new home generator wouldn't start the second time I needed it. FInally had to do without it in the dark . next day, I opened the carb bowl and it was all crudded up with white stuff. The bowl was aluminum. Now, years later It will start up even if it's been 6 months using real gas.
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Old 11-06-2024, 15:31   #13
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

Quote:
It's not the WD40. How long did/does it sit? Gas with ethanol will cause issues if not run often. I buy non ethanol gas for all yard and outboard use now. It's a huge difference.
A few years ago my brand new home generator wouldn't start the second time I needed it. FInally had to do without it in the dark . next day, I opened the carb bowl and it was all crudded up with white stuff. The bowl was aluminum. Now, years later It will start up even if it's been 6 months using real gas.
Add the blue StaBil 360 Marine to every load of gas year-round. Have been doing that ever since ethanol appeared in gasoline and never had a problem, even when it sits for 6 months or longer over the winter. Just started up my outboard running on last year's ehtanol gas treated with StaBil and it ran perfectly. Plus, be extra careful to keep water out of the gas containers.
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Old 11-06-2024, 15:42   #14
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

1. Get rid of old fuel, clean gas container so no junk going in. And get new clean fuel
2. Replace fuel filter if it has one.
3. Clean carburetor:

Not world’s greatest mechanic but that has fixed several motorcycles and outboards with similar problem.
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Old 11-06-2024, 18:25   #15
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Re: I have a 6HP outboard (Mercury) that dies at high revs...

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Originally Posted by Kettlewell View Post
Add the blue StaBil 360 Marine to every load of gas year-round. Have been doing that ever since ethanol appeared in gasoline and never had a problem, even when it sits for 6 months or longer over the winter. Just started up my outboard running on last year's ehtanol gas treated with StaBil and it ran perfectly. Plus, be extra careful to keep water out of the gas containers.
Same here. As long as the tanks are fairly well sealed I've run plenty of engines in 12 - 18 month old stabilized gas without issue, both ethanol and non-ethanol fuel.
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