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5hp 2013 Yamaha 4-stroke rough on high revs


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Hey! 

I've starded today my aux engine 5hp Yamaha after couple months of storage. It runs well on iddle and 1/2 throttle but at about 3/4 to max runs rough and sometimes chokes but does not stall.

It looks like fuel deposit in carb so maybe jet needs to be cleaned? What do you think? 

Edited by Adam
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  • Adam changed the title to 5hp 2013 Yamaha 4-stroke rough on high revs

Before fireing up the engine I've drained all old fuel till last drop from whole fuel system inc carb, emptied the internal tank and put a fresh petrol.

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3 minutes ago, Adam said:

Before fireing up the engine I've drained all old fuel till last drop from whole fuel system inc carb, emptied the internal tank and put a fresh petrol.

Did you add any fuel additive to clean the carb out? 

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1 hour ago, Adam said:

Nope mate, nothing. What would you suggest before I shall start stripping the carb out?

Others on here will know better than me on these things, but Redex for example do a fuel additive designed to clean injectors. Worth a Google? 

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run carb cleaner   from  any   motor  store    ( Halfords )    through   it   also use (  sea foam)  from  ebay   at all times     if using  E10  fuel    use a stabiliser   i use  Ethanol  Shield    from  ( Tool Station )  

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If you're handy on the tools, just strip the carb and clean it. Least then you know it's clean. I will hasten to add tho, from your description, it's unlikely to be a dirty carb. Usually, when left, it's the pilot jet that gets blocked, not the main.

I would be more inclined to think spark plug failing or filter blockage. If stored incorrectly, these will leak oil out which may possibly have got in filter.

Once carbs have started to get fuel residue build up, I have yet to find an additive that shifts it. Far better to use an additive to stop it happening to start with

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4 hours ago, suzook12 said:

If you're handy on the tools, just strip the carb and clean it....

Thanks for your answers guys. Yes, am OK with stripping carbs and stuff like that so will replace the sparkplug first and then will see how it behaves. It's a nice engine with super low hours and its annoying to see it not working as it should. Its been stored correctly. 2010 and up Yamahas can be stored on each side so small risk to get into a problems.

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47 minutes ago, Adam said:

Thanks for your answers guys. Yes, am OK with stripping carbs and stuff like that so will replace the sparkplug first and then will see how it behaves. It's a nice engine with super low hours and its annoying to see it not working as it should. Its been stored correctly. 2010 and up Yamahas can be stored on each side so small risk to get into a problems.

I was told that all main brand small engines are the same tohatsu units rebadged, and my tohatsu clearly says what way up to stow it. 

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28 minutes ago, JonC said:

I was told that all main brand small engines are the same tohatsu units rebadged, and my tohatsu clearly says what way up to stow it. 

Yes mine too. Has to lay on the handle side, which my Mercury was opposite side to the handle! 

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4 hours ago, JonC said:

I was told that all main brand small engines are the same tohatsu units rebadged, and my tohatsu clearly says what way up to stow it. 

Not sure. I've seen all the small engines known brands without the cowlings and they are totally different. Blocks, heads, carbs and all bits and bobs are different.

And yes, that's interesting that Yamaha can be stored in any way apart from upside down 🤪

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12 minutes ago, Adam said:

Not sure. I've seen all the small engines known brands without the cowlings and they are totally different. Blocks, heads, carbs and all bits and bobs are different.

And yes, that's interesting that Yamaha can be stored in any way apart from upside down 🤪

hiya mate the engine might not like that new fuel thats out i always put the expensive one in its only a couple of pence more good luck budd keep us updated

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