Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Your battery appears to be too low to start the unit. What is battery voltage when you turn key to start? If 5.5 volts, battery is too low for start.
Does the engine turn if you use the flywheel screen to turn it manually?
Jump from battery direct to the starter terminal, with ground on block. If it does not turn, I still think battery.
And this is new starter and was same with the old one? Makes no sense, and there is no place for voltage to be lost. Good ground?
Everything points to a starter that is drawing too many amps.
I see question is still open, did you find the problem?