I have a 6HP outboard (Mercury) that dies at high revs...

[Jim Cate]

Ethanol in fuel will eat anything made out of plastic.

That's odd... I buy ethanol (lightly spiked with methanol) in plastic bottles at the local markets here in Oz.

Jim

[catsketcher]

I have a nice 9.9 Yamaha 4 stroke that was not starting well - it took a more than 5 minutes of throttle to get running well at all. So I did what I always do to my two stroke outboards and pulled the carby apart and put it back together.
It took about an hour to do so but it started like a dream and then purred away. I don't use carby kits - I just pull carbys apart and put them back together carefully - the seals don't get damaged with care when pulling down.
Put air through the jets, air through the different pores on the carby body and then pop it back together. It almost always makes a poor running outboard work well. Carby cleaner, DW40, petrol, blowing with the air compressor or with your mouth - just get the thing clean and the holes open.
I just bought a new 3.3hp two stroke. The motor was very lightly used and did start but after I bought it it would only run with the choke out. So I pulled every part of the carby apart and found that a small washer was not properly arranged - it was sideways. Popped it back in and then it ran like a trooper. Might have been the reason it was being sold.
Start learning with this guy - he has great videos

https://www.youtube.com/watch?v=ye_Ui9D8dBE

cheers

Phil

[MicHughV]

I googled a repair/rebuild kit for that carb on that 6 hp Merc....and found several ranging from $14-20...
Also found an entirely new replacement carb for around $100.

Either way, rather than messing with what you got, you have options to rebuild/replace the carb....which is what I would consider under the circumstance.

Time to hit the Google button....or try Amazon

[MicHughV]

That's odd... I buy ethanol (lightly spiked with methanol) in plastic bottles at the local markets here in Oz.

Most marina's in the US don't sell ethanol laced gasoline due to past problems with ethanol gumming up various and sundry parts of the fuel delivery system.
You can only get straight gasoline, typically 90 octane or more.
Comes at a premium though.

A few area gas stations will also sell ethanol free gas, also at a premium, but not many around.

[CarlF]

I would first drain the fuel and get some "4 cycle small engine fuel". Most places that sell lawn equipment have it. Home Depot sells it at Tru-Fuel by the quart. See if an hour of running that cheers it up.

If not, it's likely ethanol fouling in the carb. 4 cycle 6hp outboards have incredibly small carburator jets that are easily cloggeg with a corrosion that doesn't reumove easily. Regular carb cleaners won't help.

1) Remove carburator and take it to a shop who will disassemble it and put it in an ultrasonic cleaner overnight

2) Buy a new carburator


The cost of these two options is about the same.

If this turns out to be it, only buy non ethanol in the future. Either the small engine fuel or go to a small airport that will often sell no-ethanol unleaded for very small planes.

The stabilizers and ethanol treatmetns really don't work very well.

[Nicholson58]

Originally Posted by Kettlewell

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.

A thousand times NO! WD40 is the worst possible product for this. It is sticky goo in a volatile solvent.

I like the collapsed fuel line suggestion. It has happened twice to me before we escaped the US and ethanol. Also, the primer pump bellows has failed four times from ethanol. (15 hp 2-stroke, 2002). Replace hoses with modern ethanol tolerant material.

We have also experienced the tiny internal fuel filter getting plugged. Dirt or a small amount of water will blind the filter. Consider adding an in line big filter with water separator bowl.

To clean a carb go to NAPA and get a 1-gallon can of carb cleaner. It comes with a basket in the can for soaking parts. Be very careful at disassembly. Count exactly the number of turns for all jets and adjustments. Don’t soak the rubber bits. Take photos. I acquired a set of jet cleaner probes but I’ve never had anything bad enough to need them.

[thinwater]

Originally Posted by MicHughV

Ethanol in fuel will eat anything made out of plastic.
Check fuel lines, filters, etc, and see if you find anything unusual

This was an issue when ethanol fuel was new, but not in the last 20 years; everything is ethanol-compatible now.


Most likely the main jet is clogged with aluminum corrosion residue. You can check the bowl for evidence. Either Stabil 360 Marine or Biorbor EB will prevent this. So will keeping the fuel really dry.


PS. Carb cleaner does not work on ethanol/corrosion deposits. A very thin wire does.

[Cheechako]

Originally Posted by thinwater

This was an issue when ethanol fuel was new, but not in the last 20 years; everything is ethanol-compatible now.


Most likely the main jet is clogged with aluminum corrosion residue. You can check the bowl for evidence. Either Stabil 360 Marine or Biorbor EB will prevent this. So will keeping the fuel really dry.


PS. Carb cleaner does not work on ethanol/corrosion deposits. A very thin wire does.

That was the issue with my Gen set. Aluminum carb bowl and build up from ethanol. I dont think I've used a bucket of carb cleaner for 30-40 years. And as you say, it's more often a jet clogged which needs a wire pushed through it.

I wonder if outboard carbs are for sale after market cheap like lawn mower carbs?
I had I think a float valve issue on my 18 HP mower carb and looking for a kit.... Amazon had a complete carb for $18 shipped! Having little time I tried it. Has been running perfectly now with zero adjustments. Just bolted it on, opened the fuel line and was in business. How can they make and sell a carb for that? There were many of them available cheap. The mower maker wanted $90 for a carb.

[Kettlewell]

Most likely the main jet is clogged with aluminum corrosion residue. You can check the bowl for evidence. Either Stabil 360 Marine or Biorbor EB will prevent this. So will keeping the fuel really dry. PS. Carb cleaner does not work on ethanol/corrosion deposits. A very thin wire does.

OTOH I have many times taken a carb apart only to find a teensy weensy piece of some crud (not corrosion related, just guck) stuck in one of the jets. Blasting it out with the WD40 has worked many times on motorcycle and outboard carbs. These 4-strokes have very small jets so are easy to plug. Another thing that can help is an inline fuel filter between the tank and the engine, if you're using an external tank.

[Nicholson58]

Carb tools.

Look for these on Amazon.

The OP problem is classic fuel starvation. Figure it out starting with easiest first:

Fuel line including squeeze ball, gas tank dip tube, collapsed fuel hose lining, water

Fuel filter, water, crud

Bad old gas

Fuel pump

Alternatively, plugs, ignition etc.

[ssteakley]

I had a similar situation and found I had a pin hole leak in fuel line from the fuel tank, it was sucking air. Replaced fuel line and problem solved.

[Capt Jimmy]

I would run 50%seafoam into engine and let it sit for a hour. Worked for me with same issue. Let us know.

[GrowleyMonster]

Red WD-40 straw for carb cleaning = good.
WD-40 for carb cleaning = not really all that good.
If you want the straw, you can get them by the hundred on Amazon.
https://www.amazon.com/dp/B07DHZRRW7
I use them for all sorts of stuff. Handy to have around.

And now back to our regularly scheduled malfunction. Outboard fuel hose and connector is an important spare to keep on hand, anyway. Get one and swap it in, and give it a go. Not quite as cheap but not a dealbreaker either is an entire new or rebuilt carburetor. A spare, all ready to go, with gasket and everything, can reduce your OOC time to under a half hour in the event of the carb getting all stuffed up or gummed up or a holey in the bowley.

I agree that WD-40 is not something that has any business sprayed in a perfectly okay running outboard, but OTOH I suspect your problem actually has little or nothing to do with the WD applied to it. Forget about the WD for a bit. Start from scratch. Give it fuel and air mixed properly and be very sure that you are doing it, and see if it runs. Good fuel hose. Good connector. Good squeezy bulb. Open tank vent. Hang your tank higher than the outboard just for good measure. Check the choke for proper operation.

Spark is spark. Enough spark to run under no load is enough spark to run under full load so I doubt if it is an issue with your spark, but it never hurts to check and maybe change the plug and condenser and points if it is so equipped and hasn't been done in more than a year or so. Check for spark is easy enough though, by unscrewing the spark plug and reconnecting the wire, and resting the plug body against the block with the carb bowl empty and fuel disconnected, and pull the starter a few times and verify that you have a nice blue spark. In bright sunlight it can be hard to see. Don't hold the plug with your fingers. It will zap the tar out of you.

So you got fuel, air, mixture, and spark eliminated. All that is left is timing and compression. You almost have to deliberately monkey with things to put the timing off. If the spark somehow got advanced too far or if there is a vacuum hose that controls the spark, there's two possible sources of trouble. But hmmmm... two stroke outboard?... has reed valves, maybe? Doubtful but something to check. Check and see if they got gummed up by gunk semidissolved by the WD and displaced into the valve. Reduced compression could make the engine run nice at WOT and no load, but see it bogging down hard and dying under full load. Just an idea. That is usually not a troublesome component which is why nobody pointed it out, I think, as well as the passing of the two stroke engine from common usage. Then again it sounds like your OB is too new to be a 2 stroke.

So when you shift into Ahead, it stalls. Is your prop fouled? The foot out of lube or full of water? You could have something as non obvious as a hundred turns of mono fishing line or something wrapped and wedged around the prop shaft. See how easily the prop turns with the trans in Neutral.

Did he spray WD into the cylinders? Or just the carb?

5BTM's suggestion sounds sensible. Check your oil level if it is a 4 stroke, and make sure you have two stroke lube mixed with your gasoline at the proper ratio if it is a two stroke as directed by the manual.

Is there an air filter? Check it. Clean it or replace it.

Probably not related but you never know and this should be replaced annually anyhow, but replace your impeller even if your engine is peeing a good stream.

Do you smell a strong smell of unburnt fuel? I keep thinking about that choke. Make sure your OB warms up good and you open the choke wide open as soon as the engine will tolerate it. Verify that the actual choke opens and closes properly when you manipulate the lever for it.

Another reason to check the oil... see if you are making oil, i.e. your sump is filling up with water or fuel. That would be indicative of a slightly more serious but still probably fixable issue. Blown out rings, head gasket, etc and hopefully not a cracked head or block. If he sprayed WD in the cylinder there is a remove possibility that it was started with WD on the piston crown resulting in excessive compression. Should be checked at least once every day that it is in use, anyway.

[searenity38]

Replace the thermal regulator. (Not the same thing as the thermostat.) I had a Merc that did the same thing. It would run WOT for 10-15 minites and then drop to idle and I couldn't get it to rev up again. I didn't stumble onto this solution until after tearing the carb apart, replace fuel lines, remove the fuel pump for testing, etc. Good luck.

[Kiwicrew]

I had a similar problem with my 3.5HP Merc. While it showed all the signs of a fuel problem, I couldn’t get to the bottom of it so I bought a new 6HP 4 stroke Yamaha. But as a last ditch effort whilst I was waiting to pick up the new Yamaha, I put the old spark plug back in the Merc. It runs perfectly now!