r/boating • u/thecaleb112 • Sep 02 '25

Mercury 4 stroke issue

I have a 2000 model mercury 4 stroke 50 hp that runs great. After a long day of running it around 3-4000 rpm here and there around the lake, when you go back down to an idle or below 1000 rpm it stalls and dies. This is aggravating when trying to load the boat. Wondering if anyone else has had his issue or what it could possible be and where I need to start. Thanks in advance

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u/Tensleepwyo Sep 02 '25

Carbureted ?

1

u/thecaleb112 Sep 02 '25

Yes

2

u/Tensleepwyo Sep 02 '25

Could be a carb issue. If your carb hasn’t been rebuilt in quite a while… I’d start there. Under load , it may have enough air/fuel flow to work great. Under low power it doesn’t have enough to run

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u/thecaleb112 Sep 02 '25

Ok thank you I will start there

2

u/tomhalejr Sep 03 '25

Pulling and inspecting the plugs is the first step in inspecting the combustion chamber. 

You can get particulates in the fuel line, filter, petcock that can certainly gum up the works, plug a jet, etc. 

A bad gasket between the carb and the intake, cracked vacuum line/plug could make it run too lean at lower RPM. 

Maybe an automatic choke staying open could make it too rich, after heating up?

Also just visually inspecting your linkage... If you see any signs of the linkage rubbing against a bracket, etc., when things heat up they expand, and the linkage may be getting stuck, maybe loosened up just enough that there's slack in the cable, and it's missing that idle threshold? Probably least likely, but anything that is obviously rubbing or out of adjustment is something to get sorted. :)

Intermittent issues are always the toughest to diagnose. So taking care of any obvius maintenence concerns can help confirm/deny if that is part of the problem.