Some issues :
Ignition coils can fail at any time, will give trouble at idle, fast idle or through the entire throttle range. Coils have 3 conditions, works good, is kaput or has intermitent heating failing issues, which is the most difficult to troubleshoot. Buy a spare ignition coil and swap between 3 cylinders, one of them is kaput, can't have 3 down coils at same time.
Main Jets for 50D2 carbs are 132 for upper and middle and 135 for lower carb. Slow Jet are 80 for all 3 carbs.
Although you can have all 3 carbs adjusted to 2.5 turns from lightly seated, it's no indication that engine will rev smooth, will need to have a musician ear for carb tunning while playing with mixture screws. Tunning with a set of 3 led vacuum gauges is more precise.
You can play with all the props you want, what you should't do is having a standard engine revving higher than its factory wot stated 5850 rpm with any chosen prop. That's the max rpm the engine was designed to run at. If it were a new engine and breaking it due to overreving forget all about Tohatsu warranty.
According to TT factory a TT installed on a 3 cylinder engine will not read accurately, are just intended to work well on 1-2 cylinder engine.