1992 43V6 turning over slowly

"I have a mercruiser 1992 4.3

"I have a mercruiser 1992 4.3 V6 in my Searay Sundancer230.I didn't use the boat about 4 years, Now, when I restar it again with a fully charge battery, the battery gauge show 12V, but the engine didn't turning over, just only say"Ta...Ta", Even remove all the spark plugs, I can't found water in the cylinders, and have good spark, So I tried with power supply connected to the battery, and the battery gauge show 16V, then the engine turning ,but slowly then before, Now I wondering if this is the problom of the Cranshaft? Piston? Starter? or others, If not, what should I check for?
Thx everyone.."

Hard to understand your questi

Hard to understand your question.

Cranks but won't start?

or

Won't crank over?

"Crank over,but need high volt

"Crank over,but need high voltage."

"If it has been sitting for a

"If it has been sitting for a long time, the cylinder walls have most likely developed some light oxidation. Even if not, the cylinders are dry without any oil. Try removing the spark plugs and squirting some oil in there, such as fogging oil. Should help it crank easier."

"Crank it w/o the plugs in it

"Crank it w/o the plugs in it like Jim said for 15 seconds. Wait 5 minutes and do it again. That will prelube the engine before starting. Get the old gas out and change fuel filters before starting. Once the engine is warm, change the oil and filter."

"Thanks gentleman, I will try

"Thanks gentleman, I will try it."

"[b]"Now I wondering if th

""Now I wondering if this is the problom of the Cranshaft? Piston? Starter? or others, If not, what should I check for?"

Ayuh,.....

Sounds like the Wiring to me,...

Remove, Sand, Clean,+ reinstall All of the Starter's Wiring, Both Positive,+ Grounds,...
I'm betting the cable ends are Corroded....

Slather'em with a coating of Grease when you're done,....
It keeps the corrosion at bay...."