I'm a beginner with motors so please bear with me. I have a 4-stroke 4hp Mercury outboard (dinghy) motor which was working fine but went unused for 3 years until recently.

It has been intermittently struggling and occasionally cutting out (as if running out of fuel) since relaunching it. I've so far changed the spark plug, changed the oil, opened the carburetor (which seemed clean and fine), checked the fuel pump, replaced the fuel filter and checked all the fuel lines.

It seems to run almost normally with the choke full out, but pushed in it struggles and cuts out after a few seconds.

Looking for ideas on where to look next.

  • 1
    Clean the carburetor properly, then test again.
    – Solar Mike
    Jul 9, 2019 at 18:06
  • I took the carburetor apart completely and cleaned it thoroughly, though I forgot to mention that in the original question.
    – Nat Ryall
    Jul 9, 2019 at 18:37

1 Answer 1


Try running it with a little choke and see if it runs better. If so most likely the Carbs need a more in-depth cleaning. Just spraying carburetor parts is enough. You have to take time to do detailed cleaning with Welder Tip cleaners or Drill Bits. But must be careful not to remove Jet material. If it's been sitting for 3 years you can count nasty Carbs.

  • I can get it to about half way without it cutting out, and it runs better at that point. I'll take it off and clean it all again, thanks!
    – Nat Ryall
    Jul 11, 2019 at 17:36
  • I did get this fixed by taking out the fuel return in the carb (which had a needle pin hole that was blocked)
    – Nat Ryall
    Sep 30, 2019 at 12:28

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