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Yamaha 150 Intermittent Stalling while Underway...Ideas on issue?

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Yamaha 150 Intermittent Stalling while Underway...Ideas on issue?

Old 08-11-2019, 09:54 PM
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Default Yamaha 150 Intermittent Stalling while Underway...Ideas on issue?

Got twin 150 yamahas that have worked great since I purchased my boat. A few weeks ago one of the engines started acting up. When I put the boat in the water, idle for a bit to allow engines to warm up, and then get up to around 4000rpm the starboard engine will begin to stall for a few seconds dropping to about 2000-2700 rpms and then risas back to 4000rpm with no throttle movement. It will do this a few times and then eventually it goes away. After leaving the boat overnight at a dock and then take her out in the morning, same thing happens. Starts to cruise juat fine and then engine rpm begins to drop down then back and then down. Not sure whats going on, had the mechanic check filters for clogging or water in the gasoline but all looked good.

Anybody had similar experience or idea ehat the problem is? It might have been coincidence but it started to occur after riding the boat with the fuel tanks pretty low. I thought it was because it was running out if gas but since then gas tank was filled and issue is still there.

Appreciate any help!
Old 08-12-2019, 03:35 AM
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Originally Posted by Redboy26 View Post
Got twin 150 yamahas that have worked great since I purchased my boat.
Anybody had similar experience or idea what the problem is?
Yamaha has made in 150 HP several carbureted 2-stroke models,
several fuel-injected 2-strokes,
and EFI four-strokes.
No doubt all of them have had similar symptoms -
but for different reasons...
Old 08-12-2019, 04:13 AM
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Mine are 2006 F150’s.
Old 08-12-2019, 04:36 AM
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Check your fuel lines. I had the same problem last year on my twin Mercs. My problem was the fuel line from the transom to the engine. It ran ok until about 3000 rmps. The ethanol fuel ate away the inner plastic coating of the fuel hose. When I gave the engine fuel, the plastic liner would collapse and restrict fuel to the engine.
Old 08-12-2019, 04:49 AM
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I agree with fishnwilliam. The fuel lines in my 2006 boat had exactly the problem he described. Fuel lines have improved since then. If your fuel lines are the silver lines with red lettering, those are notorious for this problem.
Old 08-12-2019, 05:21 AM
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I have the same engines and had a similar issue last season. Started out as Intermittent loss of rpm and over time the engine wouldn’t even start. Mechanic had a tough time diagnosing because you needed the issue to occur while he had it. I started guessing at issues. Turns out it was a short in the optional water pressure sensor. The short caused the main power supply for all the sensors to drop which gave the ecu odd readings. Solution was to disconnect the water pressure sensor - it’s nice to have but not necessary.
Old 08-12-2019, 10:29 PM
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Originally Posted by fishnwilliam View Post
Check your fuel lines. I had the same problem last year on my twin Mercs. My problem was the fuel line from the transom to the engine. It ran ok until about 3000 rmps. The ethanol fuel ate away the inner plastic coating of the fuel hose. When I gave the engine fuel, the plastic liner would collapse and restrict fuel to the engine.
I’ll check them out to see what I find. The strange thing is it usually happens when I first get out. When I head back to port engine runs solid. Almost as if the issue was gone only to happen again the next day going out.

Thanks for the input
Old 08-12-2019, 10:31 PM
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Originally Posted by 36309 View Post
I have the same engines and had a similar issue last season. Started out as Intermittent loss of rpm and over time the engine wouldn’t even start. Mechanic had a tough time diagnosing because you needed the issue to occur while he had it. I started guessing at issues. Turns out it was a short in the optional water pressure sensor. The short caused the main power supply for all the sensors to drop which gave the ecu odd readings. Solution was to disconnect the water pressure sensor - it’s nice to have but not necessary.
How do I know if I have a water pressure sensor and where do disconnect it? At this point willing to try anything.

On a separate forum a few folks were saying they had issues with the primer bulbs and the internal check valves. Anybody had this happen? Could it also be a source of the issue?
Old 08-12-2019, 11:23 PM
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Injectors. Remove the injectors from the good motor and put them in the bad motor, and vice versa. Free troubleshoot for 15 minutes work.
Install a large 10 micron fuel filter to prevent recurrence after you put refurbed injectors in. Good luck!
Old 08-13-2019, 01:22 PM
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Originally Posted by SeaPro48 View Post
Injectors. Remove the injectors from the good motor and put them in the bad motor, and vice versa. Free troubleshoot for 15 minutes work.
Install a large 10 micron fuel filter to prevent recurrence after you put refurbed injectors in. Good luck!
Do you think if it was a faulty or clogged injector that I would have it happen more often? The stalling usually happens during the ride out to the sandbar. I usually stop, wait a few seconds, throttle back up and most of the time the issue is gone. On occasion the stalling, stopping, back on throttle happens 2-3 times. But then like magic, its gone, rest of the day engines run fine.
Old 08-13-2019, 03:05 PM
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Yes you're right. It would happen all the time, so it's probably not the injectors. That is where I would start, though. An awfully lot of times it's the injectors with F150s. It happened to me, and it's free except the 15 minutes to swap them.
You have the best diagnostic tool in that you have a perfectly functioning motor with which you can swap parts. The injectors could stand to be changed regardless. Less us know when you solve it.
Good luck, Bud!
Old 08-13-2019, 03:57 PM
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Track down the fuel line from the tank to the engine connection and make sure there are no kinks in the hose. This happened to my friends boat on his F150. Had to pull the engine cover to find it.
Old 09-02-2019, 06:03 AM
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Finally got this resolved. VST filters extremely dirty and clogged. Cleaned them out and ran great this weekend. Thanks for all the troubleshooting ideas.
Old 09-02-2019, 06:30 AM
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I was just about to type VST filters, then saw your reply. Good on you for solving it.

While you're at it, change the fuel filter on the front of the motors too.

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