Engine turning over very slowly

[carsonmurph1]

I have a 1972 Mercury 402E long shaft that hasn’t started since it came out of storage for the winter. When I turn the key to start the engine it will turn over, but it turns over pretty slowly. It acts in a similar way to when the battery is almost dead. Using a multimeter I checked the voltage on the battery is 12 volts, the voltage at the end of the wire harness going into the engine is 12 volts. The voltage going into the starter solenoid is 12 volts as well. Is there something I’m missing here? Given it’s a 1972 model year engine parts are extremely hard to come by and expensive if you can get them. Does anybody have any ideas on what could be wrong and any tests I could do to verify what’s wrong before I start buying parts? Thanks

 

[carsonmurph1]

Update: The voltage going into the starter solenoid is 12 volts, the same that the battery outputs. However, the voltage coming out of the solenoid fluctuates between 4 and 6 volts when the engine is cranking. Does this mean its a bad starter solenoid? Thanks

 

[Geshka]

Try to verify following:
1. Remove plugs and rotate flywheel by hand. Do you need extra force to do that ? Oil in cylinders might get too viscous and there is too much of resistance. Spraying into cylinders diesel/acetone mix will help to "unfreeze"
2. Wire jumpstart cables directly to the stater bypassing solenoid (ignition off) and see if starter engages flywheel and rotate it properly.

 

[airshot]

If the battery is actually reading 12 volts then you battery is almost dead!! Full battery should read 12.6 volts or higher.. At 12.3 volts a battery is half dead, anything 11.9 volts or less is considered dead. You need to charge up your battery to start

 

[Scott Danforth]

Clean all your battery cable connections

 

[jimmbo]

Update: The voltage going into the starter solenoid is 12 volts, the same that the battery outputs. However, the voltage coming out of the solenoid fluctuates between 4 and 6 volts when the engine is cranking. Does this mean its a bad starter solenoid? Thanks

Perhaps, but that isn't the only place a Voltage drop can be caused, weak Battery, bad Cables, loose/dirty Connections, as previously mentioned are also suspects

 

[AVI_8]

Firstly do as Scott said, then give the battery a good charge, as @airshot said 12 volts is very discharged, a fully charged 12 volt battery when it’s been fully charged should read about 14.4 volts when just off the charger.