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Old 16 July 2018, 08:31   #1
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Yamaha 150hp Engine help

Hi all,

Newbie here. I have been searching the web trying to pin down a specific Problem I am having with my 4 stroke 2009 Yamaha 150 outboard for some time now. This forum has been a gold mine for information.

The problem:
The engine starts perfectly and gets up to full speed on flat water on my 5.8m RIB. Once the swell builds up all it takes it one light/medium bang on the bow from a wave and the engine instantly starts making a grumbling noise, slows to about half speed and vibrates. It's as if the bangs is throwing somthing off inside.

I have had new injectors installed and still the problem persists. When this happens the hand pump bulb on the fuel line also goes soft, having some one pump it can bring the engine back to normal functioning pace. Could air be getting into the fuel line perhaps?

Usually if I stop the engine and restart it she is perfect until just the right "bang" from a wave and it throws out again.

Yesterday when it happened my top revs were 3600 while it was thrown out and it was giving a lot of vibration.

Any ideas on this would be great as I would like to clearly instruct my mechanic when I next have him as to what might be causing it.

Cheers
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Old 16 July 2018, 10:40   #2
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Can you run it on a full portable 25litre tank? Is it possible there are apricots getting in when the banging occurs?? Does it run perfectly well for along as there is no banging?? Nik
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Old 16 July 2018, 11:04   #3
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Some part of your fuel system must be breaking down, sucking air or similar, as above rig up an independent fuel supply and test. If the same same fault happens again maybe start by checking the fuel pump.
Good luck
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Old 16 July 2018, 11:34   #4
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Quote:
Originally Posted by matata View Post
Can you run it on a full portable 25litre tank? Is it possible there are apricots getting in when the banging occurs?? Does it run perfectly well for along as there is no banging?? Nik
Good idea to have an independent tank ready to hook up anyway.

Just keep any apricots away from it, they're nasty little things.
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Old 17 July 2018, 05:35   #5
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Quote:
Originally Posted by matata View Post
Can you run it on a full portable 25litre tank? Is it possible there are apricots getting in when the banging occurs?? Does it run perfectly well for along as there is no banging?? Nik
Great Idea. I will try and run from an independant fuel source and see how she reacts to the same conditions.

The engine is 100% on flat water. Usually no issues until I get out of the harbour and then take the first proper bump.

Can I ask What apricots are??

Thanks for the help guys.
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Old 17 July 2018, 05:38   #6
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Apricot
From Wikipedia, the free encyclopedia
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This article is about the trees and their fruit. For other uses, see Apricot (disambiguation).

Apricot and its cross-section
An apricot is a fruit, or the tree that bears the fruit, of several species in the genus Prunus (stone fruits).

Usually, an apricot tree is from the species P. armeniaca, but the species P. brigantina, P. mandshurica, P. mume, and P. sibirica are closely related, have similar fruit, and are also called apricots.[1]
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Old 17 July 2018, 05:39   #7
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or crap in your fuel tank that is blocking the flow!
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Old 17 July 2018, 09:47   #8
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Hi
It sounds like you have debris in the fuel tank. While on a flat sea the dirt remains away from the pick up pipe but as the boat moves about more from the swells, then the dirt will move towards the pipe and block it. That would probably explain why the primer is soft. As others have said, use an independent tank
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Old 18 July 2018, 05:43   #9
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Thanks for the help guys. I will test with a spare tank this weekend and see whats what.

Appreciate the help.

Alex.
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