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Jeff G.
Jeff G., Marine Mechanic
Category: Boat
Satisfied Customers: 4726
Experience:  42 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance
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I have a Yamaha 1
, Saltwater Series II 150HP 2 stroke,

Customer Question

Customer: I have a Yamaha 1
JA: Thanks. Can you give me any more details about your issue?
Customer: Saltwater Series II 150HP 2 stroke, with only 46 hrs. Idle is rough and won't sustain, does the same both cold and hot.
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Submitted: 1 year ago.
Category: Boat
Expert:  Jeff G. replied 1 year ago.

Can you fill me in with exactly what the engine does or doesn't do and it's history?

Is this a recent problem? Does it make a particular sound? Does it accelerate? Good top end?

Has the engine been sitting or did this just happen?

Customer: replied 1 year ago.
Jeff, I bought the boat three months ago. I'm located in the Philippines, ambient temperature is around 30 deg C. Engine starts well cold, but won't sustain an idle, either hot or cold. From initial 600-700 rpm, engine will die in less than 15 sec. On idle, sounds rough, as if not on all 6 cylinders. Once warm when shifted into gear, accelerates smoothly, runs fine above 1000rpm, top end has plenty of power. It's difficult to use when mooring or anchoring as engine won't keep running.
I inspected all plugs, replaced with new although they were fine, no difference. To eliminate possibility of bad or stale gasoline, tried running on portable 6 gal tank, same problem.
Engine was new in 2010, boat was owned by retired Dallas fire captain in northern Mindanao. Boat was kept in shed, only 26 hrs run in 5 years, as he had problems launching boat. So yes, it did sit for long periods of time. When I test drove boat before purchase the problem wasn't evident, so I suspect that it is new. Since purchase, boat was shipped on trailer by RORO ferry to Manila, then trans shipped on 40' flat rack as hold cargo on conventional freighter to Puerto Princesa. Once there, it was towed 100 km on trailer to launch point where road is closest to my private beach. Its possible that vibration during transit may have loosened some adjustment, as I noticed that the loctite on the full retard adjustment screw was broken - screw is in approx half way position. Since initiating this query, I have located and downloaded a service manual and will adjust the full retard and idle per that manual when I next go to my beach house later this month.
Engine model is 150FETO, serial 6G4 L(###) ###-####D.
Expert:  Jeff G. replied 1 year ago.

It does sound as the linkage is not correct.

Your engine is a little different from the engines here in the US so I don't have a service manual or parts book that is a direct match for your engine.

That being said have you tried to adjust the idle mixture screw on the top side of the carbs?

Remove the air silencer from the front of the carbs and make sure all the throttle plates close equally and open the same all the way.

the 600 to 700 rpm is that in neutral? In the water? If so your engine is idling too low. Raise the idle speed to about 950 in neutral in the water, when you put it in gear the rpm will drop a couple hundred rpm and you should have a good even idle. This too could be from mis adjusted linkage.

Post back what you have. We can work from there.

Customer: replied 1 year ago.
The 600-700 rpm is in neutral.Based on what you have said, together with what I read in the service manual (can be found here: ), what I plan to do is this:
1. Adjust the full retard screw per service manual, then loctite to prevent further movement.
2. Warm up engine.
3. Loosen cam screw, adjust idle to 950 in neutral using throttle screw on middle carb, retighten cam screw.
4. See if that solves the problem. I suspect that it will.One thing that I didn't mention is that the engine tends to overheat (warning comes on) if idled for more than about 10 minutes, so that top me confirms that the retard setting is incorrectly set.I'll get back in touch late this month to give you an update after doing work outlined above.
Expert:  Jeff G. replied 1 year ago.

I would also replace the water pump impeller and thermostats.

I think once the linkage is adjusted correctly and raising the idle you will be fine.

Let me know how it does.

Customer: replied 1 year ago.
Jeff, I'm now back in the city after almost a month at the beach. Progress report - I reset the timing to factory specs, that didn't help. If anything it made it worse, engine would not idle at all. In desperation I removed the top carb, and found fine sand in the float chamber, with pilot jet plugged. The center and bottom carbs were even worse. After cleaning all three and reassembling, I removed the fuel filter, and found a small split in the filter mesh. I replaced the filter element, engine now runs great, starts easily, idles well. It now has an extra 30 hrs running time.
Expert:  Jeff G. replied 1 year ago.

That isn't sand in the float chamber but is a byproduct of old fuel. As the old fuel evaporates it sometimes reacts with the aluminum and other chemicals in the fuel causing this. Try not to use any fuel over a few months old, particularly in a fuel tank outside. I'd also recommend manually draining the carbs after each use by removing the drain screw in the float bowl. Drain into some paper towels.

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