Mercury 80 hp 1978 dies when in gear from idle

Some examples on how my Mercury dies when I go into gear.
2 scenarios;
1) "Good" setting of idle screws (inbetween the two stalling points). The engine starts very easy but also dies instantly when I engage the gear.
2 "Worse" setting i.e more "fat". I adjusted the idle screw by a 10th rev each time. Then I got bored and turned out 1/4 with two tries. Then the engine "lasted" longer in gear in comparisson. Thus the idle where rough and I needed to use the choke for starting. If I turn out more my engine will not start.
The carbs are clean (removed and washed/soaked in solvent followed by ultrasonic cleaning and last drying by pressurized air). The compression is OK around 9 bar and max diff is 8% between cylinders. New BUHW-2 sparks. New diaphragm in the pump. Changed the exhaust baffle due to leak (into cyl 3 and 4 but is good now). The butterflies are in sync. Coils are OK (resistance OK). I have not measured the Top Voltage Peak yet (I am waiting for parts to do my own DV adapter).
It runs well when I manages to get it to run in gear (I need to repeat to engage the gear twice. the second time it will run due to the small momentum it gets from the first egagement). I can do full throttle and it runs up to top speed without any hesitations. It runs very well in all rpms and even if I run slowly for a while trolling. It does not take as much gasoline per knot as my former boat.
BUT I cannot make it to run when I engage the gear - I need to do that twice to get away?!?!
Suggestions?
Bad propeller? Still some error in ignition? Or still fuel related?