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8hp yamaha outboard issues

Noah Fitzpatrick

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Had the boat out the other day, got 1k out from the ramp, and the motor cut out suddenly, and then wouldnt start for 5 mins. It happened about three or four times again before i called it and went back in. Noticed that the primer blub was struggling to pump fuel, and was very slightly sucked in when i was moving. Valve on the tank was open so it wasnt causing a vaccum. I could prime it but it was a lot harder than usual, and then it would run for another minute or so at full throttle before chugging and then dying again. Has this happened to any of you? I am thinking either a blockage in the fuel line, dodgy fitting on the tank end, or possibly a blocked/dirty fuel filter???


Thanks in advance.

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Starving for fuel.....external breathers away from the tank might operate well at the breather but not down the line at the tank. if it is a fuel cap breather it should vent well.

Fuel lines can break down quickly esp if they are the wrong type of plastic and react to alcohol fuels.

Primer bulb vales do fail internally.

If it is hard to prime with the bulb you should replace that if you are confident your breathers are functioning. Your bulb should never look partially sucked in.

Prime with the fuel cap off....if it primes ok it is a venting problem.

Air locks in breather lines do not usually starve an engine from fuel.....it simply sucks that fuel back to the tank.

A kinked or pinched fuel line will also stop the engine quickly....check the line had not worked under something pinching it off.

If all the above fails check inside your tank that it has a mesh end on the pickup tube...if it does not there could be something in the tank blocking the pickup. 1 medium sized fish scale can really do your head in trying to diagnose it blocking the inlet and you can't see them in the fuel tank.....so if you really have the shits with someone....

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i had a closer look this arvo, took the fitting on the motor side off and attempted to pump fuel but couldnt get any flow/fuel whatsoever (with a full tank as well). took the pickup out of the tank and the mesh on the end is still there with no holes. The primer bulb will push air out but then suck it back in?

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End of the fuel line when dsconnected will have a spring loaded ball to shut off the fuel flow when disconnected....you need to wedge it open to try the bulb.

If the bubl does not work I would presume it is faulty and jammed in the valve.

Easy test is to remove the bulb and blow back to the tank...if it blows back easy it will be the bulb.

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  • 2 weeks later...

checked fuel line and filter, no issues there. called up stones corner marine and they reckoned carby straight away. Wasnt too keen on the 5 week wait and the inevitable hit to the wallet though so went and got some carby cleaner, watched a few vids and took it apart. bit of cleaner in the jets and gallery, compressed air, and i chucked it back in. 

Was a very nervous first pull but she started straight away and ran sweet at idle for 15 mins or so, back on the water the next day.

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A word of caution, compressed air can ruin a carby by excessive force on some check valves and or force a clog further inside. When using compressed air blow across any opening, not straight into it.

Plenty of carbies have tiny wafer thin plastic check valves pushed deeply inside then you often can not see. Compressed air easily damages these and they are generally not replaceable.

Good to hear you got the engine running again....time will tell if it was the issue.

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2 hours ago, Noah Fitzpatrick said:

Lucky the big compressor wasn’t working then and I had to use the tiny one for blowing up mattresses I guess haha. Pretty simple little things in the small two strokes by the looks of it though? 

You said early in the post that the primer bulb was sucked in??? The offender made it to the carby?

Anyway, happy days and happy boating 👍

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