1977 Mercury 200 20HP stalls at high speed, what could cause this?

Question

The motor runs good at idle and half throttle, but when I go to full throttle it starts missing and shuts off. Does anyone know what would cause this? it's a 1977 Mercury 200 20HP S/N: 4713724

Answer 1

Sounds to me like a fuel delivery system problem.

You need to check for cracked fuel/air lines, maybe a kink in one somewhere. I can't recall if that particular engine uses a fuel pump, or an air pressure system, but at any rate, all of that needs to be in top working condition to deliver the amount of fuel you need to run at full throttle.

When was the last time you changed the plugs, and or wires? It could be an ignition problem. Inspect the wires for any cracks as well. How about a tune up? When was the last time you did that? Are you running old fuel? Is it a mixture of old, and new? Are you using Quicksilver oil?

All of those factors could have something to do with it. Look them all over, and see what you find. You may just have to take her in, and have it given the once over.

Happy boating!

Stevo.

Answer 2

Has it been sitting long?Try putting the chock on when running fast. it might pull water or trash out of the carb?When running fast squeeze the prime bulb if Eng runs better than it's a fuel problem, If the bulb goes flat the the vent Or cap in or on the tank pluged,Take the fuel cap lose? Changed fuel filter lately,on Eng also.Sound like a fuel issues?Good luck

Answer 3

The high speed jets in your carbs are the first jets to plug up. They are probably clogged(very common). There is no throttle position sensor on an engine that old, sorry Andrew.

Answer 4

check your throttle positioning sensor along with your intake manifold and your plugs and stuff like that.

Answer 5

i would guess lack of fuel. Try a new pump, Bigger line, or check your vent in your tank.