See full version: How to manually turn over a mercruiser
A good tip is to unplug, inspect and plug back in the main harness plug back at the engine. This is a big black rubber "cannon" plug. The pins in the plug or socket can fail to make contact. Clean up the pins and socket holes. Push the plug firmly back into position but use care not to overtighten the hose clamp. Over tightening the plugs hose clamp will ruin the plug and/or socket.
If you use a little jumper wire and jump across the large Red wire and the Yellow/Red wire the engine should crank. It won't actually start unless the key is on or if you have also jumped the Red to the Purple lead. If the engine cranks when you jump the Red to Yellow/Red lead; but it does not crank when you use the Key Switch, it means you have a bad Key Switch. more
If your gauges activate but the engine makes no clicking or cranking noise when you turn the key to the START position, you might have a bad In-Gear-Starter-Protection-Switch. This switch is locted in the remote control. If the shifter is not in nuetral or if the switch is bad, the engine might not crank. Try wiggling the remote control handle in and out of gear a few times and it might work. here
Key Switches go bad. It's a moving part and water can get down into the switch. The Mercruiser Key Switch has three terminals on the back. One is a large Red wire which is the main positive feed. Another wire will be Purple which is "ignition". This feeds the gauges and keeps the engine running. The third lead is Yellow/Red and it is what activates the starter slave solenoid to crank the engine. more
4. Your battery and starter motor. Batteries are only good for a year or maybe two at best. Start off with a fresh battery. Make sure your starter looks good and turns free. more
5. Drive Lube and Engine Oil. Make sure you have enough of good clean lube and oil in BOTH the engine and the sterndive unit. Change any old or contaminated oils and filters. here
Consider the following items:
Letting your boat sit for a long time without being run is a bad thing. There are several items which should be addressed BEFORE placing your boat back into service. If you simply drag your boat to the ramp without taking care of these importnat items you will most likely break down, overheat or have some kind of trouble.
Secondly, what does tilt trim mean? In the “tilt” mode, the system raises the engine completely out of the water when not in use. It can also be used to raise the engine when running the boat slowly in very shallow water to prevent propeller damage. In trim mode, the system works to adjust the angle of the engine to affect the running angle of the boat. more
Likewise, how do you manually raise an inboard outboard motor? here
Grasp the bottom of the outdrive behind the propeller. Pull the outdrive up and hold it until the person on deck ties the rope onto a cleat, completing the manual raising of the Mercruiser outdrive.
What is tilt and trim on outboard?
Don't use starter fluid or pour gas down the carb. That's very hard on engines and can tear the motor up before you even get it started. [links]
Now check the carb. It's great if you have a good clean one you can switch out for the old one but that's not always possible. What you don't want to happen is suck nasty stuff from the bowl through the carb.
If the air cleaner hasn't been on it or if there are a lot of open holes, stuff may have gotten in it. Pull the carb and look down into the intake. If you see anything, pull the intake off and clean it out and look down into the intake ports of the heads. more
It's time to see if the motor will turn over. First take the distributor cap off so you can see the rotor. Now take a breaker bar and socket and get on the crank bolt and see if you can turn the motor over by hand. more
Now the cylinders should be lubed up. Turn the motor one more time pushing the excess oil out. here
Most of the time you have heard "It's supposedly rebuilt," or "It was running great when we quit driving it. "