mercruiser breaks up after about 5 minutes running

[cookiesareyummy]

Mercruiser, v-8. conventional ignition, carbed. I don't have a year or number as engine was replace a few years back.

The engine starts up great and runs as smooth as anything. After about 5 minutes of cruising the engine begins to break down but runs great if you leave it below 3200rpms. I tried a full tune up, cap, rotor, points, condenser, plugs, plug wires, I tried the coil just to make sure it wasn't breaking down, I changed the fuel filter.

When it breaks down it doesn't do any sort of popping, it just begins to miss and lower in rpms, not sure what to do next, any ideas? Engine is not overheating, checked it with a temp gun.

 

[bitterboater]

Re: mercruiser breaks up after about 5 minutes running

Is the fuel tank removable? There might be moisture\debris in the fuel. How old is the fuel? Have you tried cleaning the Carb.? You might try running a can of SeaFoam through the fuel tank next time you go out.

 

[Beefer]

Re: mercruiser breaks up after about 5 minutes running

Pretty much the same problem I'm having. You say you changed a fuel filter. You may want to check to see if you have more than one. There is one at the fuel pump, and at the inlet to the carb. Does it have a fuel/water separator? Check that as well. When it starts to break up, what is your choke doing? Could be the choke is not working properly.

Just some things to check.

 

[LVANGEE]

Re: mercruiser breaks up after about 5 minutes running

Which fuel filter did you change ? Water seperator ? Be sure there is not a filter up on the carb at the end of the line going into carb . If this filter is plugged it will make the motor run poorly from lack of fuel .

 

[6meter]

Re: mercruiser breaks up after about 5 minutes running

Which fuel filter did you change ? Water seperator ? Be sure there is not a filter up on the carb at the end of the line going into carb . If this filter is plugged it will make the motor run poorly from lack of fuel .

I would say be sure there IS one at the carb. And check to see if plugged. Could be a dirty carb also. Crap does get into it, even with filters.

 

[cookiesareyummy]

Re: mercruiser breaks up after about 5 minutes running

Everyone was looking in the right direction of it being fuel.
I started it up with a clear hose going from the tank to the remote filter and found bubbles when the engine was running. I replaced a few connections at the tank and the bubbles went away, ran the engine out on the bay for a while and it didn't act up. Thanks for the help everyone : )