weak cranking power

[oddysea1]

I have a 1989 200 h.p. Yamaha twin engines the port engine has a weak crank when trying to start and then peters out after 8 seconds or so.I replaced the battery, switched out the starter and starter solenoid from the working engine and still have the same issue.Any suggestions on other possibilities or on a trouble shooting plan would be appreciated.Thank you Andy

 

[99yam40]

check all connections from the batteries to the motor including the negative.
even cables can go bad internally.
voltage drop test under a load should show where the high resistance is

 

[tommarvin]

You should have a battery switch, so you can start each motor with both battery's.
Like the man above, this is a battery cable problem, and it's probably the ground, clean and make sure all grounds are tight with nylon locking nuts.