Yamaha 15hp 2-stroke wont idle

[Lake-Effect]

Originally Posted by MicHughV

I think fuel is often the culprit, may be worth it to have a fine mesh fuel filter on top of the tank when filling up.

When doing the service this year, i pulled out the outboard's own fuel filter to peer inside. Our filter has a fine metal screen, not a soft filter media, and when I backwashed it with carb cleaner (first time ever)... stuff came out! Just a few particles of plastic, dirt etc... but an eye-opener as to what can make it in, even when you're careful.

[Tspringer]

This crap just does not get better…

The 5 hp brand new in the box unopened Mercury, arrived today we got it on the dinghy and I’ve tried everything known to man with this brand new motor absolutely will not run.

So now we are cancelling guests, sailing to Nassau and taking this PoS Mercury back for a full refund. No idea what after I get my $ back, might just return to the states. Sorta over it at this stage, just not worth it

[carlwk3c]

Could be cracked diaphragm in the fuel pump. Remove, disassemble, inspect. Had this issue on a Tohatsu 9.8 4 stroke. Same behavior.

[lestersails]

On my purchase last fall of a new Tohatsu sail pro (which I think is the same block as your Mercury) it would start and run just a few seconds, then die. Turns out they gave me the wrong fuel tank, so the connector at the engine did not match. I thought that if it was a Tohatsu line and the connector fitted, it was the right connector, but I guess not (or maybe it was just defective?) Anyhow, they replaced the tank and line and it runs perfectly.

[wrwakefield]

We have a 2005 Yahama 15hp 2 stroke with original carb, etc. Still starts right up and runs like a banchee... [We are full time cruisers.]

We have always added Seafoam (1 oz/gallon of gas) to the fuel when filling the tank and jugs. (High marks from Practical Sailor as well...)

Seafoam preserves the fuel, and apparently keeps the carb happy... (I should say carbs as we have been doing this for decades for all our fuel for ATVs, snow blowers, lawn mowers, portable generators, etc. and never had carburetor issues... Of course we use premium fuel filters as well.)

I should also note we have never used any fuel with ethanol added- in case that is a factor as well... (I don't know... Thankfully ethanol laced gasoline isn't available in our cruising grounds over the past 15 years or so...)

FWIW

Cheers, Bill

PS: I like the idea of having a spare carb on hand just-in-case. You mentioned finding one on Amazon. Is it convenient to share that link? (We have very weak internet at the moment...)

[P3sailor]

Could be a few issues here. If using fuel with ethanol your issue could also be a partially clogged fuel line. Ethanol breaks down the inner lining of the fuel line which can collapse and restrict fuel flow to the engine.
Most of the time the problem lies within the carburetor jets. You can clean the carb all you want but until the jets are removed and cleaned mechanically the problem will persist. I've used a strand of copper wire from some old wiring to clean the jets, works well and doesn't damage the orifice like steel or other metal that's harder than the brass jets. Good luck with your repair.

[P3sailor]

Sounds as though it could be an operator problem. First issue, "brand new, in the box."

[Lake-Effect]

Originally Posted by P3sailor

Sounds as though it could be an operator problem. First issue, "brand new, in the box."

Yeah, personally speaking I'd want a dealer to unpack and fire up a new outboard, and demo it to me, before I carry it away. Not always possible of course.

[wholybee]

I am not familiar with this carb, but will share what I have learned in general.

First, do not use metal picks or wire. Many of the orifices are very precisely sized and a metal tool can enlarge them and mess with the tune. Use monofilament fishing line. You should have some as small as 2-3lb test for some of the small holes.

Most carbs have a well. I'm not referring to the bowl, but a separate, smaller chamber, maybe cast into the main housing, and maybe with some other cover and maybe not. The well is a low pressure area, between the main jet, and the ventrui. It is where the liquid fuel ideally evaporates and turns into a gas. There will be VERY tiny air bleed holes into this area. 2lb test fishing line might be too large for these holes. They have caused me lots of grief on several carburetors. You should locate them and make sure they are clear. Sometimes there is a brass tube somewhere with tiny holes in it. The tube itself is the well, with the holes the air blead holes.

If the main shaft in the carburetor wears and leaks air through the bushings, then the carburetor is done and needs to be replaced. This should only be on very old carbs.

Then of course do all the normal cleaning of the jets and passageways. But I wanted to point out the well, because those holes are tiny and easy to miss, and will cause all sorts of running problems.

[BBill]

Originally Posted by MicHughV

When you say buying " new" in Nassau I'd check the manufacturer year made stamped on it before forking over yer dough...'jes sayin'......

Are you aware that ob mfgs (at least Yamaha and Merc in the beginning) did away with mfg yrs automatically being the same as model yrs? When this started they had factories full of unsold engines mfg yrs earlier and marketed them as the current model yr. Crazy but that started in the mid 2000s. They converted all new old stock to the model yr they were actually sold. It was common to see a 2004 mfg date on the showroom floor sold as a 2006 model yr. Consumers had no clue they were buying old engines.