4hp 4stroke mercury outboard very difficult to start

[Dick Kobayashi]

This may be helpful or maybe not. The passages in a little carb like yours are very small. I solved a starting/idling problem by replacing the carb my self. Pretty much a bolt on job. Cost $100 and my time. If pure gas does not work you might try this.

If you go the pure gas route - start fresh with 100% pure gas. You will know right away if it works.

I know this is not popular but I think that the problem is not gas per se. And I don't think it is the cold either. Just an opinion.

For pure gas - go to any fixed base operator at a local airport. They will have a pump.

[radsailor]

I think what I will do is buy a small can of 4 stroke non ethanol gasoline, pump out whatever gas may be in the internal fuel tank and put the fresh stuff in the internal tank and try to start the engine using the internal rather than the external tank. That will be a quick inexpensive test. If that does not solve the problem then I need to get the carburetor cleaned. I cannot do this while the motor is hanging off the back of the boat and I live in an apartment with no garage so no place to do it myself. And, I am totally inept mechanically with no proper tools. Would rather pay someone to do it right the first time although the mechanic at the boat yard swears it was running great so will bring to a mercury dealer.

[mgphl52]

Personally, I'd just put the ethanol fuel in a regularly driven vehicle and search for ethanol-free fuel.
From looking at the Pure-Gas.org map you should be able to find ethanol-free fuel within an hour or so drive.

[radsailor]

If I have to drive an hour each way, I would rather just buy it at Lowes or Home Depot

[radsailor]

UPDATE
I emptied the internal fuel tank and put in ethanol free gasoline. Made no difference. Spoke with a Mercury dealer mechanic who said the motor should start in any weather.
Probably the carburetor but could be the fuel pump.

[bgephart]

I will bet anything it is the carburetor. I have a 6HP 4 stroke Tohatsu, and I have to clean the carb every 5 - 6 months to assure reliable starting, and I always use non-ethanol gas. There are several videos on YouTube that show how to do it. I am no mechanic, but I have learned to do it in about 1 hour. The orifices in these 4 stroke carbs are so small it is amazing anything gets through them. When this baby dies, I am going to get a used 2 stroke - I ran those for years and years with no problems like this 4 stroke.

[radsailor]

So today was a beautiful day for Winter sailing in the Southern Chesapeake area. I was determined to go, motor or no motor. I would take my chances sailing in and out of a very narrow channel. But, before I did that, just for the heck of it, I removed and drained the fuel filter. The motor started right up ! I shut it off and tried again- no luck.
I removed and drained the fuel filter again- started right up. When I was done sailing, the engine started right up.

Clearly there was some junk in the fuel system (although I did not see anything) that was blocking fuel flow.
Hopefully the issue is fixed, but if it happens again, I am going straight to the fuel filter.

[mgphl52]

You might want to carry a spare or three...

[jen1722terry]

Question while we're on the ethanol-free gas topic: I have a small container of ethanol gas treatment aboard. Only had to use it once. Do these treatments really work?

Cheers

[radsailor]

Rather than pour more money into the damned engine, I bought a Torqeedo.
Fantastic !

[Dick Villamil]

I have the 3 hp mercury and the previous owner had the exact same problem. I put in a new properly gapped plug then emptied the tank of the old fuel and used only non ethanol high test fuel. I also found that he never opened the vent on the gas tank and when I discovered this I did a test and with the vent opened the motor runs great but with it closes it starts then dies due to the lack of fuel flow. After doing all of this the motor starts on the first or second pull and runs great.

[Kailua Kid]

Start fresh. The ethanol-free gas does not attract moisture. You do not want any ethanol in your tank or in your engine, at all. I have not had to pull apart a carb for years, maybe a decade, since I stopped putting gas with ethanol in my small engines (outboard motors, chainsaws, weedwackers, pressure washer, etc.). It only works in automobiles because you use it up before it has a chance to attract moisture, which then turns to an opaque, syrupy substance that plugs up the jets and other tiny orifices in the carb. If you are scrupulous about keeping ethanol out of any engine that sits for a week or more between use, you will be amazed at how well everything starts-- and then continues to run.

[S/V Necessity]

As far as the comparison between the OB and your leafblower, your mechanic *could* be correct. There is such a wide variation in how a small engine could be designed and tuned that it's not a apples to apples comparison. With a carbureted engine tuning can be an art. For example, I used to have a motorcycle that I changed the intake and exhaust on, and I rejetted the carbs. I managed to get it to run ever so wonderfully, but it would go out of tune when you went down a hill and hit a shady cool place (colder denser air). In it's stock form it wasn't that touchy. But by changing the exhaust and the intake I had mucked it all up for daily driver use. (But it did make more power!)

So it wouldn't surprise me that a leaf blower manufacturer would design the engine to run well in a wide temperature range (especially since they commonly double as snow blowers), and that an outboard manufacturer might design around the assumption that it would only be used in fair weather.

Something simple you could try, add something to the air intake that will slow down the air flow just a tad. If it's a foam filter I might slip a layer or two of t-shirt material ontop of the foam. (on my motorcycle we added socks over the individual intakes). Otherwise your mechanic may need to change the jet in the carb. (This of course assumes you are positive your carb and fuel is clean.)