Short story= I switch feet and it worked.
Long story= I’ve been riding for almost a year and still struggled free mounting. I learned to ride by holding onto a pole first (like almost everyone). I always placed my left foot on the pedal (6 o’clock) held pole then placed right foot on other pedal (12 o’clock). After a couple of months of learning to ride in general I felt it was time to learn free mounting. By the way at this point I’ve moved to a 27.5 wheel.
To free mount I would place left foot on at 3 o’clock and then mount up to catch the right pedal as close to 9 o’clock. This kinda worked about 1 in 5 times. The big problem was to often I ended up putting to much weight on that left foot and the uni would fly out from under me.
One day it occurred to me that my body was trained to put weight on my left foot from back in the countless days of pole mounting. I switch over to starting my free mount with right foot on first and got it the first time. Now it’s working 8 out of 10 times. Hope this helps someone. Cheers
Something else to think about in terms of that. Instead of thinking about how much “weight” to put on the pedal, turn it around. Just keep your foot in that position relative to the seat.
Seems ridiculous at first, but really that’s all you need to do. Don’t push down, don’t let up, just hold your foot in place. With a little practice, this becomes very easy, and keeps your mounts from reverting to the kind where one foot is at the bottom and you’re trying to ride away from the dead spot. 
I cannot really understand what “turn it around” means.
Can you explain with a short vid? I usually start making an half idle before leaving or make a jump to start weighting on both pedals in the same time.
“Turn it around” in this context does not refer to physically turning something round. It means “look at the problem from the other direction”.
Instead of doing X to achieve Y, concentrate on Y and X will happen naturally — that sort of thing.
So, instead of concentrating on how much weight to put on your foot in order to ride better, turn the idea around and just try to keep the foot int he right position and the weighting will sort itself out.
The solution to most riding problems is to ride more. It takes a while to get used to shorter cranks. Until you’re used to them, they can occupy so much of your attention that you ride worse than you were doing with the long ones. Every rider has an ideal crank length for their level of experience, their style of riding, and so on. Chasing after the idea of short cranks as an end in itself is fun, but will not make you a better rider, but becoming a better rider will make you get more out of short cranks.
Ok, now I agree with you. Everithing seems less difficult just practicing than focusing on it too much
Think different
Thanks John your advice works well.
@vogelfrei I also tend to focus to much on a problem instead of letting it solve by itself.
I like your advice of not thinking about it from a weight problem.
Sometimes when I focus too much on not putting weight on that foot I end up putting weight on it. Cheers!