1973 50hp mercury runs awful under load

[kclanier]

Motor runs great in the yard, and RPM's run up with the idle throttle fine
In the water in gear it runs awful. It will run up to about 25% power.
Throttle all the way forward and it dies. It shakes but no strange noises.
Help please

 

[Laddies]

Re: 1973 50hp mercury runs awful under load

Check for a dirty cap and rotor, then check the timing

 

[acdcbcwhatever]

Re: 1973 50hp mercury runs awful under load

Check for water in cylinders. My 150 does the samething, pulled the plugs out, and found a water gray plug in number three. Also run it with water hooked up and see if it spits out the back of a carb.

 

[adam89k]

Re: 1973 50hp mercury runs awful under load

Motor runs great in the yard, and RPM's run up with the idle throttle fine
In the water in gear it runs awful. It will run up to about 25% power.
Throttle all the way forward and it dies. It shakes but no strange noises.
Help please

It could be simple, check that the vent on your gas tank isn't pluged then check if your choke is coming full off it might be staying on abit wich would cause the motor to shakes cause its trying to keep up with all that fuel.

Also double check to make sure your fuel mixture is perfect.

Good luck.

 

[Chinewalker]

Re: 1973 50hp mercury runs awful under load

Sounds to me like you're running on two cylinders (of four). More than likely it is a plugged carb, as one carb feeds two cylinders. Multi cylinder motors will "rev" just fine with no load and can fool you into thinking nothing is wrong, but in fact, under load, the problem becomes apparent.

What are your compression readings?

Check the plugs. Do the top or bottom two look different from the other two?

What happens if you place your hand or a rag over the mouth of one of the carbs while running?

I'm not real familiar with the ignition systems on those motors, but a spark check would also be in order.

- Scott