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Old 06 August 2019, 08:50   #1
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Outboard knock on full throttle, any ideas?

So ,I recently purchased a Honda BF5A 2009 but have noticed that it makes a knocking sound when Iím planning at full throttle so I have to back off a tad. It also seems slightly underpowered, it seems to only just get on plane with me (11 st) on my zodiac 275 RIB.

Iíve been running with new fuel and a new plug.

Any ideas would be greatly appreciated.

Cheers in advance,

Dan
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Old 06 August 2019, 10:12   #2
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A 5hp is right on that will it won't it plane situation so yes it is low powered. But exactly what is your Zodiac... a GRP hull RIB or an air floor SIB?? And what HP is it rated for?

Regarding the knock it shouldn't do that... but are you sure it's the powerhead or gearbox or just something ancillary rattling? For example my outboard lock can rattle at certain speeds to the point you'd say the engine bearings had gone... but just put your hand on it to damp the sound and it's quiet.
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Old 06 August 2019, 10:29   #3
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You need to check it out...but, I have a Honda 2.2hp outboard and a Honda generator and they both knock like buggery on full throttle and full load.
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Old 06 August 2019, 11:43   #4
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Originally Posted by Fenlander View Post
A 5hp is right on that will it won't it plane situation so yes it is low powered. But exactly what is your Zodiac... a GRP hull RIB or an air floor SIB?? And what HP is it rated for?

Regarding the knock it shouldn't do that... but are you sure it's the powerhead or gearbox or just something ancillary rattling? For example my outboard lock can rattle at certain speeds to the point you'd say the engine bearings had gone... but just put your hand on it to damp the sound and it's quiet.
Hi mate, yeah itís a proper rib with v keel so should be easy to plane I would imagine. Re the motor, it sounds like itís from the motor itself, its a consistent knock when Iím full throttle planning but I guess it could be something else, annoying thing is it only does it when it planning (should of mentioned that before!) so I canít even get near the engine to listen for it as I have to be up the front of the rib.

Cheers
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Old 06 August 2019, 11:44   #5
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Cheers Jwalker, atleast I’m not the only one with this issue haha hopefully one of us find a solution/ reason for it happening.
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Old 06 August 2019, 13:23   #6
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.. hopefully one of us find a solution/ reason for it happening.
IIRC both my Honda engines have a fixed ignition timing of over 20 degrees so I think they're a bit advanced for full load and full throttle, if I back off the throttle slightly they soften up noticeably. When starting them I have to be very deliberate and not hesitate on the cord pull cos they fire early and will rip the cord out of my fingers and it fekin hurts!
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Old 06 August 2019, 13:28   #7
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I'm shocked... see para 4 on page 47 of this instruction book...

https://cdn.powerequipment.honda.com...s/31ZV1634.pdf

I'd really not want to operate an OB at sea that does this and I'm amazed Honda think it's "normal".

Have you tried Super Unleaded?

What's the RIB rated to... 8hp... 10hp? Might be nice to look towards a slightly larger motor.
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Old 06 August 2019, 13:54   #8
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Can’t seem to open that link

I did wonder about super unleaded, I will give it a go! Also been told esso supreme is the best because it’s ethanol free.

The RIBs rated at 8hp but it’s really old and only a 2.7m so I wonder if they mean a 8hp 2 stroke which would be much lighter.
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Old 06 August 2019, 13:56   #9
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Interesting! I’m not very engine savvy tbh but I’ll have a read on that. Mines the same, if I back off a tad the knocking stops.
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Old 06 August 2019, 14:02   #10
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Have you managed to open it now. Even if I find it weird it does seem to say it is "normal" for that engine.
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