Starter runs sooo slow

"Have a mercruiser 1986 mr170

"Have a mercruiser 1986 mr170 in my draco.Problem when I try to start, the starter goes so slow round. And sometimes it just says "click".. Battery is new,fully charged and the starter is also new. Even tried with power supply connected to the battery, same problem.. This is the engine model with no dynamo or belts.. Electronic voltage regulater instead...
Just wondering if it's supposed to be like this? If not, what should I check for?
Thnx on advanced.."

"Ground the coil HV lead to th

"Ground the coil HV lead to the block, remove the spark plugs and see if it will crank.

Is the antifreeze level normal? If you find water in the plug holes, get it out, change the oil and filter and find the leak. Cracked manifold would be a first guess. If no water is found and the motor turns a little faster then I would suspect loose or bad battery cables, defective starter, weak battery or all of the aforementioned.

"Battery is new" means you just bought it. It may have sat on a shelf for 3 years. What is the mfg. date code on it? H6 code means August 2006.

If it won't crank w/the plugs out, take the battery back to where you bought it and have it "load tested". If it passes the load test then you have other problems."