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1978 Merc 500 Turning over too slow to start.

B

Bob in Tennessee

Contributing Member
My Merc will spin what seems to me fast enough to start, but it won't. When I hook a battery charger to the battery, the engine spins fast and starts. After running a while, the engine starts easily throughout the day. The Marine Starting Battery is almost new and checks out with a load tester. Is there some other way to test battery?
 
My approach would be to take starter apart / inspect / do ohm check on armature.----Very easy to do and costs no beer tokens.
 
The load tester is pretty much bullet proof in determining the condition of a battery. What you can do is to remove the connections on both ends of the battery cables and clean them up bright and shiny then reinstall nice and tight. Any corrosion you find, like at the (ground in particular since the hot lead is on a copper shaft) ensure that you wire brush off. I'd do that before I tore into the starter as its easier.
 
Load testing battery is not 100% ! Bought 2 type 29 battery's for my RV and one would not hold voltage overnight.(load tested myself) Carried it back to Interstate and they checked it. They said just needs charged and I had something draining it. They charged it and load tested and said it was OK. I carried it back home and tested it again before installing. Store is only 20mins away and it was low again(8volts) so carried it back and they swapped it out, said connection in battery was bad
 
While digging into cable connections, it was obvious wires were in sorry condition all the way to the engine plug. I ordered a new harness and will do a complete rewire and then see if problem solved, or mess with starter.
thanks for the advice!
 
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