The half throttle/full throttle thing might be due to some subtle things wrong with your throttle linkage. As the pedal goes down and the carbs open various levers and rods go through various levels of increasing and decreasing leverage, making the throttle plate to pedal movement a changing relationship. And the throttle on the carbs themselves aren't linear.

You might want to adjust the linkages to make the throttle open less in the first part of the pedals travel. I had to tinker with the linkage on my DCOE's for a while to get them right. Originally it would open the throttle all the way when the pedal was down, and close it all the way with the pedal up, but it too would unleash 90% of the power in the first 50% of the travel, and had little sensitivity within that first 25%.
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