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Mercury 50hp 2stroke/ low on power

Escortdan1991

New member
Hi I’ve recently bought a new boat with a mercury 2stroke 50hp, with quicksilver controls. the boat is from mid 90s and engine serial number I think is (09629963) ? Took it out yesterday and it starts instantly, and idles well, I have no rev gauge.. but at I’d say half throttle it trundled along lovely all day long! When you try to go faster it’ll sit on the plane for 2 minutes then shudders and tries to die ( recovered by dropping the throttle) my mind points straight to fuel starvation but although mechanically minded have not worked on outboards. Fuel lines outside the engine are seemingly ok and plastic filter looks new. It had new plugs at beginning of this season. Happy to delve in but want some direction first. ( putting the boat in water to test is quite an ordeal so want to eliminate as much as possible before trying. Sorry for long post, trying to be comprehensive. Thanks. Dan.
 
Clean the carburetors first.-----Blockage in a carburetor can ruin a 2 stroke motor.-----A new impeller is a good idea on a " new to you " motor as well.-----Did the motor sit for many years ??
 
Clean the carburetors first.-----Blockage in a carburetor can ruin a 2 stroke motor.-----A new impeller is a good idea on a " new to you " motor as well.-----Did the motor sit for many years ??
Engine has only sat since March, with new impeller being fitted prior to my purchase (with proof and a good flow of water from engine)
ill whip the carbs off and give a good clean. Will I need new gaskets or anything to reassemble?
Is there any adjustment in the control unit? Heard somewhere about dodgy neutral switch or something. Cheers
 
The nuetral switch has to do with safety.-------If control is in gear the motor will not crank !!-----That switch does nothing when motor is running.----The nuetral switch is not your problem.----Inpect fuel tank innards.----Inpect diaphragm / check valves in fuel pump.----Perhaps borrow another tank and hose for a test run.
 
The nuetral switch has to do with safety.-------If control is in gear the motor will not crank !!-----That switch does nothing when motor is running.----The nuetral switch is not your problem.----Inpect fuel tank innards.----Inpect diaphragm / check valves in fuel pump.----Perhaps borrow another tank and hose for a test run.
Ok thanks, glad we cleared that one up, was about to blame the neutral switch for all of life’s problems 🤷*♂️. Tank and hoses outside of engine are all new. So will inspect/clean carburettors and pump.
(On a side note, is the fuel primer hand pump purely for starting or can you run without it providing it starts?)
 
The purpose of the primer bulb is to fill the carburetors.----Saves the starter motor from having to do that via the pump on the motor.----Or saves your arm / shoulders on a manual start motor.-----So once the motor is started the primer bulb does NOTHING and does not need to be there.
 
I will be taking the carbs off my 40 Merc for cleaning; I have bought carb gasket kits and fuel pump diaphragm kits from marine engine - ships quickly.
 
Ok thanks, glad we cleared that one up, was about to blame the neutral switch for all of life’s problems 路*♂️. Tank and hoses outside of engine are all new.
Were the fuel lines that were replaced,have a 3/8" / 10mm. bore? Too small and you get restriction.5/8" or 8mm will do but I prefer to go that wee bit OTT.
 
Were the fuel lines that were replaced,have a 3/8" / 10mm. bore? Too small and you get restriction.5/8" or 8mm will do but I prefer to go that wee bit OTT.
Need a little advice... when removing all the cowlings from the engine so you can see the head of the two carburettors. Without the engine running I moved the throttle position to full but only the top carb butterfly opened... should they not both open at full throttle or is the second carb on a vacuum when the engine is running? Cheers
 
On my Merc 40 2 stroke 4 cylinder, there is a mechanical linkage that moves both butterflies at the same time; I think there is a synchronization procedure in the shop manual to make sure that both open the same amount; there are no vac lines to the carbs.
 
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