Stalling when in gear

[SSDWD]

Hi folks ! New to this forum. I have a 1973 Pacemaker with fresh rebuild.
I’m having an issue with stalling at idle when I put port motor in gear
I can start it relatively easy Idles beautiful. Revs great.
Put in gear and it stalls at idle speed.

I’ve done the following.

Added water remover
Seafoam
Fresh gas
Blew the siphon valve
New fuel filter
I checked for vacuum leak at carb
I adjusted jets and idle
Carb had a new kit just put in
I’ve changed some plugs rest still looked good.
I can still spin shaft by hand.
Checked filter in carb. Clean

Any advice would be greatly appreciated

Safe boating everyone!

Turk

[Nicholson58]

Transmission and prop free to rotate? My variable pitch prop will stall the engine if it’s too steep

[SSDWD]

I can still turn it by hand

Seems to be rotating okay.