50 HP Mercury Running Half Throttle

[Orion Nebula]

My 50 HP Mercury will only run at half throttle. I have replaced the powerpack, coils and trigger but am still only getting half throttle. I tested the voltage on my powerpack and am getting 295 volts from the stator side and around 150 from the coil side. The compression on all four cylinders is around 130 psi. I am getting spark on all four cylinders. Any ideas on what the problem could be?

 

[racerone]

Re: 50 HP Mercury Running Half Throttle

Is this something that happened suddenly ?-----------Plugged exhaust ?-----------Bad lower seal on crankshaft ?-----Plugged carburetor ?---Broken linkage between the 2 carburetors ?------Leaking fuel pump ?----Flooding carburetor ?--- Check to see if both carburetors open fully.----Does the manual fuel pump go hard on start-up?

 

[Orion Nebula]

Re: 50 HP Mercury Running Half Throttle

Yes, this happened suddenly before I replaced the parts. I have also replaced the fuel lines and cleaned the carburetors. What do you mean by the manual fuel pump going hard on startup? I don't believe that I have any of the other symptoms that you mentioned but I can check them out.

 

[racerone]

Re: 50 HP Mercury Running Half Throttle

When you operate the bulb for start up does it go hard ??---------There is something wrong with your motor and only some simple trouble shooting will get you the answer.---Assuming and guessing does not work in most cases.

 

[Alumarine]

Re: 50 HP Mercury Running Half Throttle

Do you mean that if you push your throttle farther than half way your motor won't run?
Or do you mean that it only runs when the throttle is half way?

 

[Orion Nebula]

Re: 50 HP Mercury Running Half Throttle

Racerone, yes the bulb gets hard at startup. Marc c, when you push the throttle more than half way, it will still run but it runs like it is at half throttle.

 

[Mi duckdown]

Re: 50 HP Mercury Running Half Throttle

Serial number? What was the problem, before you changed all those parts

 

[Orion Nebula]

Mi duckdown, I had the same problem before I replaced the parts. Serial # 6586642

 

[CharlieB]

Lack of fuel flow will also limit motor RPM and power.

Disconnect the fuel line to the carbs, point it into a suitable container, crank the motor and see how well it pumps. You should find a nice fat pulsed stream.


If air manages to be sucked into the system from a poor fitting, leaky O-ring in a fitting, cracked hose, loose clamp, etc. The pump will not be able to provide sufficient fuel for the motor to fully perform.

Replace the fuel hose to the carbs with a clear hose, run the motor and watch to see if air bubbles are passing through. If so, then there is an air leak, find it, fix it.

Once finished be SURE to remove that clear hose, it IS NOT APPROVED FOR FUEL, only as a very short term testing tool.

 

[Mercurylips]

According to Mercury, It is a 1974.