5hp 2-stroke Yamaha outboard won't idle

[Gerry]

I am trying to resurrect this five-year old outboard that I haven't run for two years. I have changed the fuel and fitted a new spark plug and cleaned the carburettor three times, replacing the two most delicate gaskets (£40 - ouch!) even though they looked OK. Still, it won't start without choke and won't idle but only runs at very-rattling high speeds. If I jam it into gear, and if it doesn't stall, than it seems smooth enough and powerful.

I used Wynn's carburettor cleaner (mostly ether, it seems) and have blown through all the tubes. Someone said the parts need to soak in cleaner for at least an hour, so that is my next step.

What am I missing?

 

[Iliade]

Strip the carb and give it a water bath in an ultrasonic cleaner. Blow through all of the sometimes microscopic airways, preferably with a non-HSE approved 100psi air line (wear eye protection and sweep up first so that you can find the bits you inevitably blow across the floor.) What you are trying to remove may include varnishing, zinc/magnesium/aluminium oxide, congealed fuel bugs and seahorse poo, so no one cleaning fluid is likely to dissolve it all.

Try the Wins again.

(Of course, there is bound to be some seal or plastic component that objects to the carb cleaner)

Refit and see how it goes.

Then give up and buy a new carburetor.

Modern 4T motors are becoming notorious for this. 2T less so, but...

 

[Lakesailor]

Is the float level too low? Have you checked it?

 

[TQA]

Strip the carb again and look for the slow running system. It has a screw in needle valve usually called the air adjusting screw in the Yam manuals.

Screw it in counting the turns and remove it. Blow through the slow running system making sure you have cleared out any obstructions. If it remains blocked rod with fine wire. I know this is not recommended but the next step is a new carb.

Reassemble making sure the slow running adjustment is the same no of turns out.

This is a very common problem and it may be corrosion that is blocking the slow running passages, if this is the case it is really hard to shift and a new carb is often the only option. No amount of soaking in magic potions will shift it.

 

[VicS]

Strip the carb again and look for the slow running system. It has a screw in needle valve usually called the air adjusting screw in the Yam manuals.

Screw it in counting the turns and remove it. Blow through the slow running system making sure you have cleared out any obstructions. If it remains blocked rod with fine wire. I know this is not recommended but the next step is a new carb.

Reassemble making sure the slow running adjustment is the same no of turns out.

This is a very common problem and it may be corrosion that is blocking the slow running passages, if this is the case it is really hard to shift and a new carb is often the only option. No amount of soaking in magic potions will shift it.

Yes Id think you are on the right track.

There is also a jet associated with that slow running system ( called the pilot jet I believe in the carb diagrams ) I'd clean that carefully with a soft copper wire as well as cleaning the passages in the carb body which you describe. Nylon monofilament might be suitable for poking through these.

Is the float level too low? Have you checked it?

and be aware that there is a tiny clip linking the needle with the float arm

 

[mtb]

never put wire or any thing through carb jets you will damage the jet only use high pressure air
I use paint gun thinners to clean carbs before I strip em it is much cheaper than cans of spray, I deal in carburetters for my meager living and sell quite a few jets because people ruin em
As others have said it does sound like a blocked jet because ( when you use choke it starts and wont low rev )

I have a 5hp yamaha which acts like this when it's been left for a year or so. I give it time to sort it's self out the petrol evaporates leaving a varnish or because of the different metals you get corrosion most of the time the petrol will desolve the white powder. Once running the engine settles down, their very reliable but it breaks my heart to state that after 6 years I have just recently had to buy a new impeller for the pump £8 omg £8 I'm not impressed and feel cheated, I have always cared for the engine leaving it stuck on the outboard bracket in all that lovely sea air never using fresh petrol until It uses up the old stuff

 

[VicS]

never put wire or any thing through carb jets you will damage the jet only use high pressure air
I use paint gun thinners to clean carbs before I strip em it is much cheaper than cans of spray, I deal in carburetters for my meager living and sell quite a few jets because people ruin em
As others have said it does sound like a blocked jet because ( when you use choke it starts and wont low rev )

I have a 5hp yamaha which acts like this when it's been left for a year or so. I give it time to sort it's self out the petrol evaporates leaving a varnish or because of the different metals you get corrosion most of the time the petrol will desolve the white powder. Once running the engine settles down, their very reliable but it breaks my heart to state that after 6 years I have just recently had to buy a new impeller for the pump £8 omg £8 I'm not impressed and feel cheated, I have always cared for the engine leaving it stuck on the outboard bracket in all that lovely sea air never using fresh petrol until It uses up the old stuff

Thats why I said carefully with a soft copper wire. It wont harm a brass jet.

As for pump impellers you'd expect to replace them periodically ...... I never hear any complaints about replacing flexible vane impellers in an inboard engine coolant pumps. Many people would replace them routinely anyway. For some inexplicable reason people expect a similar impeller in an outboard to last forever.

 

[Gerry]

Success! Thank you so much. Particularly grateful for the fishing line tip.... Running really sweetly now.

 

[Jimmyjames]

I know this is really old now but I'm having similar problems. How did you solve the issue?