Crank but want start

[Wellcraft1996]

1996 Welcraft Excel26 Mercruiser 5.7Liter V8 engine. It has fuel has ignition spark but still want start. Starter seemed to be struggling turning engine over so I replaced with new starter. Now with new starter engine acts like it wants to start but want. Batteries are fully charged but the engine sounds almost as if engine stuck/frozen up. What is going on with this engine?

 

[Bondo]

Ayuh,..... Yer starter issue sounds like yer battery cables, 'n/ or their connections are corroded,......
I'd start by cleanin' both ends of both cables to shiny metal Clean,..... 'n try it,....

You are supplin' water to it, Right,..??
All lube oils are Full,..??

Is it carbed,..?? 2bbl. or 4bbl.,..??
Efi,..??
Mpi,..??

 

[Wellcraft1996]

Ayuh,..... Yer starter issue sounds like yer battery cables, 'n/ or their connections are corroded,......
I'd start by cleanin' both ends of both cables to shiny metal Clean,..... 'n try it,....

You are supplin' water to it, Right,..??
All lube oils are Full,..??

Is it carbed,..?? 2bbl. or 4bbl.,..??
Efi,..??
Mpi,..??

4bbl carb and battery is fully charged. I try the battery post cleaning

 

[Bondo]

4bbl carb and battery is fully charged. I try the battery post cleaning

Ayuh,..... Both ends of both cables,....

 

[Wellcraft1996]

Ayuh,..... Both ends of both cables,....

Battery fully charged, dont have post on battery. Pulled number 7 cylinder plug and it was wet with gas or oil black stuff.