1976 Mercury 20hp motor Serial # 482178

Hey guys. Im trying to find the starter for this motor. When I hit the button, the starter will spin the flywheel one stroke and then pause before it does it again. It doesnt keep her pulsing long enough to fire. Kinda acts like its not getting enough juice from the batteries. I have two brand new batteries run in parallel with 4awg battery cable so I know its not a power issue. I got this motor off Craigslist and the guy said it was a brand new starter but it had only worked 4-5 times, then it just quit. Kinda makes me think he put the wrong starter on... I can pull start it on the first try but it has a two piece cowl thats a pain to put back on and the cold duck season is on its way. I'd like to be as lazy as possible... Any motor gurus out there that can tell me where I'm going wrong?

Double check all your connections.Bypass starter solenoid & jump directly to starter to see if you have a connection problem.Also check to see how starter gear is messing with flywheel to make sure its not binding.I have same motor in 1979 vintage.