yamaha 150 troubleshoot ?

[Gojetsgo]

Hi, a bit puzzling...turn key ON, bendix gear on starter engages the flywheel but cannot turn it to start the engine. Checked/validated fully charged batteries/new batteries, all connections appear clean and tight. When I put cables direct from battery to starter the engine starts up. Then while moving forward and trim down the engine cuts out. However when engine is off, the tilt/trim works. To summarize; when I connect direct from battery to starter engine starts, when I trim engine cuts out. When engine is off, the tilt/trim works, So am thinking the starter is good, the tilt/trim is good...from there on I'm stuck on what to check next to fix this. As always, appreciate the counsel. Thanks in advance.

[99yam40]

bad connection at battery, or motor, or a bad cable

[ausnoelm]

Connections “appear” clean and tight is a clue, they must be known to be clean, not just appear clean, remove them and check, while they are off, check the cable itself.

[Keithbaja]

Time for a Voltage drop test

[Gojetsgo]

will do and confirm outcome....appreciated