Hello, I have a 25hp 2003 mariner which apparently is simillar to the 25hp mercury.I use the following proceedure to start mine from cold.

1. Squeeze the fuel line bulb untill it is hard.

2. Pull out the primer knob(situated on the front of the motor)slowly one or two times and leave the knob out.

3. Again squeeze the fuel line bulb just to make sure that it is hard.

4. On the ignition switch turn the key to the right and press it in this will operate the electric choke. Keep it pressed in and then start the motor.

5. Once the motor starts push in the engine primer knob or the motor will stall after a few seconds. .

6.Lift up the warm up lever approx no more than

1/4 or 1500rpm untill motor is warmed up.Then push it down.

I appreciate that every motor or is different even similar models. Hope this helps.