2004 four stroke 40 hp Mercury 40elptefi doesn't turn over

[RandyJ]

2004 40 hp Mercury 4 stroke. Starter won't crank engine. Acts like it has too much compression but only 100 psi evenly on all 3 cylinders. Battery 12.8 volts. All cable connections clean. New solenoid. Even jumping solenoid I get same results. I've adjusted valves to factory specs. Starter seems strong on bench test. Just not overcoming compression to turn engine over. It has been sitting up a couple of years. Before that it would be hard turning over first time then I could bump starter and it would start right up and run like a champ. Anyone have a clue what is going on or how to make it easier to turn over????

 

[Jperkins]

Sounds like the starter may not have enough torque and struggling to turn the motor. It can bench test good and still be weak. I'm far from. an expert but had that problem with a jet ski.

 

[airshot]

Have the starter tested or your just guessing. Also have your battery load tested, just because it checks 12.8 resting, it may have an internal short that can drop that voltage below minimum voltage when a load is added on...

 

[QBhoy]

That’s extremely low compression numbers, without looking up what it should be…I’d be certain that most 4 strokes would be way higher. Just roughly and generally, I’d say most would be above 140 for sure and more likely about 160+.

 

[flyingscott]

Does the flywheel turn freely by itself

 

[RandyJ]

Does the flywheel turn freely by itself

Not exactly sure what you mean but trying to turn the flywheel by hand feels completely normal.

That’s extremely low compression numbers, without looking up what it should be…I’d be certain that most 4 strokes would be way higher. Just roughly and generally, I’d say most would be above 140 for sure and more likely about 160+.

That's what I thought too after reading several posts but I don't have any reference to look it up. However, since it had been running fine and compression is almost perfectly even in all 3 cylinders I tend to think it is ok. After sitting so long without cranking I'm thinking possible no oil on rings may be allowing lower compression. First I need to resolve this starter issue. The timing belt is kind of loose so I'm wondering if that is possibly causing this hard start problem. I have a trencher with a Honda motor that was really hard to turn over until I adjusted the valves.