Johnson 25 outboard motor?

I have a 25 Merc. listen to `` J `` check fuel lines , assuming it``s 50:1 mix the oil turns to sludge in the fuel lines, especially if the float ball window is yellow.

This is simple. The fuel line has to hold pressure, otherwise the carb runs dry. Lacking fuel, the motor will cough, spit and cut off, just like you described.

Listen close at the fittings for the wheezing sound of sucking air while you pump the primer bulb.

If that doesn't help, just replace the whole fuel line with bulb and fittings. Those things wear out after awhile anyway.

Alternatively, you can buy a new bulb and quick-disconnect fittings to install on the hose you have. The male fittings on the tank and motor will pretty much last forever. They for sure outlast a portable fuel tank, and the one on my 1979 vintage motor is original and still going.

If the bulb still loses prime, take the air silencer cover off the front of the motor, till the motor full up, pump up the primer bulb and keep squeezing. Don't try to burst it or anything, just apply some pressure. If you see gas running out the carb throat, it means your float valve is worn out or misadjusted.

Otherwise, start replacing the fuel lines on the motor (fitting to pump, pump to carb). Somewhere in there is an air leak, it's just a matter of time until you find it.

Usually is the carb. Could be the filters, the float, jets, throttle needles or just mechanical failure of a fuel system part, like a carb.

If everything checks out and works , spark plug, pump, lines, filters, then look at the carb.

Some have a Diaphram for choke, could be that, could be the Bowl Float, I am thinking it is carburetor. I do not know if it is two or four stroke, that kinda matters, a fine inspection of all the parts is needed. Could be as simple as a cracked or rotted bulb or diaphram, could need a carb rebuild, might even be the fuel or fuel deliver systems.

Coffs, spits and cuts off. Remove the spark plugs to see if there are water droplets or fuel droplets on plugs.

Water droplets could mean water in fuel or a leak somewhere between cooling system and cylinders.

Cure for water in fuel system is to drain fuel tanks, the fuel line, the short fuel connector line on motor to fuel pump, the fuel pump and the line into the carbs and the carburetor.

While you have the fuel pump apart look at its diaphragm for wear and holes; I would replace diaphragm. And put stuff back together and refill tank with new gas/oil mix.

Now run motor and check see if that cured problem. If it did not, I would remove the cylinder head and its gasket. Look at gasket for splits, cracks, holes. Replace head gasket with new.

Then check the thermostat and its gasket and replace.

If there is a goodly amount of fuel clinging to the spark plugs do this.

Make sure the choke is becoming full open, horizontal that is when you remove choke after the motor warms up after starting motor.

With knowing choke is functioning properly, do this next.

Remove carburetor from motor and then remove the lower portion called the sediment bowl. This gives you access to the fuel system workings. Look at at the back of the float. Remove pin that holds float to carb body. Remove float. The inlet needle valve should have come out with float. If not look into the hole and remove inlet needle. Check hole for dirt and other stuff, clean with solvent or a stick you custom make.

Then look at the inlet needle. If there is a ring around near the point the needle valve both the valve and the seat or the other brass thingy it lives and works in need to be replaced.Reassembly is reverse of dis assembly.

You have to do this one thing after installing float. Check float level. It should be level with surface where you removed float sediment bowl. If not, bend the tab in back of the float to make float sit level.

Then remove high and low speed jets to make sure they are clean plus the hole where they live and work in. Clean and put back, reassemble carb. Be sure to put in a new gasket between sediment bowl and carb body.

The fuel line and it's bulb loosing pressure? Replace fuel line. Check every piece of fuel line and fittings used to connect parts. Fuel line segments should not have cracks. Fittings should be tight. Replace if not.

The fuel pump and it's diaphram you checked and replaced earlier.

Other things to check are if you added and mixed oil to your fuel. And if you have opened a vent if supplied on your fuel tank before starting motor..

And I would replace the spark plugs if they are carboned up or moist. Be sure to set gap on new plugs. A good sales person can do that for you when you buy spark plugs.

Replace the hose connection or the O/rings in the connections they leak and suck air. Loose prime in bulb. When done run gumout in the gas.

Check the fuel filter....If your motor doesn't have one..check the screen in the fuel pump..sounds like it's starving for fuel

BEFORE YOU DO ALL THAT SUGGESTED ABOVE SUGGESTED STUFF, ...check the fuel line and the bulb in the fuel line for cracks & loose clamps at the joints !

Make sure the vent on the gas tank is open

take it to repair shop

dare i assUme you replaced spark plugs,,replaced wires,,cleaned carborators,,,Basic stuff like that,,replaced fuel filter?? well did you punky