25 hp Mercury 4 stroke will not start or starts extremely hard.

This is a 2 stroke engine - an outboard motor?

Two strokes are quite robust. The usual mistake people make with these engines (think of chainsaws, lawn mowers and hedge strimmers..) is to use car engine oil instead of the correct two stroke oil. Motor oil is completely incorrect and fouls the spark plug.

The other fault is to mix fuel and two stroke oil in the wrong ratio. Most chainsaws etc .. use a mix of 25:1 Too much oil causes oiling and misfiring of the plug. Too little oil causes excessive and fast wear.

Your engine starts up. That tends to suggest that everything is working ok up to a point.

However, look on the following link which deals with an overheating problem for that engine:

http://www.etecownersgroup.com/post/25hp-etec-problem-6107593

Disconnect main fuel line to engine, attach hose and put other end in suitable container, run pump to start siphon action. Or, begin tank removal if that is your plan and pump is inop., insert hose into large tank opening where fill hose has been removed and use compressed air and rag into same hole to begin siphon action. USE EXTREME CAUTION!!!

Dude....putting 2 stroke fuel into a 4 stroke engine is just silly, but not where your problem lies. Check the coils to see if it is generating spark...if not then check the ignition module....even 'oily' the plugs should fire.

Check that gas line is clear, check fuel filter (if any) is unclogged, make sure gas tank is vented properly (in the old days, through the gas cap), pull float bowl and check float valve that it isn't plugged,

Pump the tank dry of the fuel using the electric fuel pump, just jump the fuel pump relay to get the pump to run and remove the supply line to the injectors and attach a hose. Use extreme caution around gasoline, no sparks, ground the container to the truck.

a car will run fine with most evap system broken so thats not problem if turns over but wont start ck for spark, fuel power to fuel injectors any ground wires you may have ran into running hoses . the anti theft and ecm also .

Vehicle manufactures have made it extremely difficult to remove fuel from tanks. There are several ways, all not too easy. Try pick up a connection the fuel supply line either under the car or in the engine compartment and see if you can pump the fuel out of there, If the fuel pump is in the tank and has an anti siphon valves in it, this will not work. The other method then is to remove the rubber connection that connects the tank to the filler pipe and push a pipe into the tank from there.

Hi, here's the plan. First check for a drain plug on the tank. If that's a no-go, disconnect the fuel supply line to the cold start injector as shown in the picture below. Use a funnel to guide the fuel/water into a catch pan. Turn on the key to run the fuel pump and watch as the catch pan fills. Turn off the key to empty the catch somewhere safe, and redo until the tank is empty. After the tank is empty, add a couple of fresh gallons of fuel and pump it through to clear the residue. Then reattach the line to the cold start injector and refill the tank. Power up the pump again and give it time to fill the line before starting. Then give the kids a stern warning.
Thanks for using FixYa.

Hello. If you remove the fuel filters and fill them with fuel, then hold the accelerator pedal to the floor while cranking the engine it should start. If that does not work, spray a little starting fluid (ether) into the air intake while cranking, just use the ether sparingly. This should get you going again, good luck.

Check the coil out put.
Loosen the wires from the plugs with the engine off then find some plastic plyers or an insulated tool to remove the wire without getting shocked.
Start the car and one by one remove and replace each wire to see which one does not make a difference in the way the engine runs. Thats the one that probably has a bad coil.