The green/yellow designation refers to the safety features, not the chisel shape.
They recently switched their stock bar/chain to a cheapo .050 ga. bar, so they may have not gotten a lot of .325 .050 chain loops yet.
Make sure that all of the bolts that attach the transmission to the frame are all there, if the ones in the front fall out then everything will flex the more load is on it, like going uphill. And the flexing may let the belts slip.
I see that you said that you went back to the old fuel line, then try just richening the low mixture screw.
It would be the one on the top right.
You may need to pull off the plastic limiter.
It is a purge bulb, should return fuel to the tank, no need to fill, it pulls fresh fuel through the carb, purges the air out.
The fuel lines on this model are real hard to mess up.
Don't be alarmed that the clear fuel filter looks empty, most folks go that rabbit hole at least once.
While running, apply the choke partially, and see if it clears up.
I remember back in the 1990s, I saw a couple of their mowers made by Murray, and I remember having trouble getting the parts looked up. I'll look out in the shop tomorrow for some old Murray books.
It is pretty bad when the small engine mechanics can quit and go to work at McDonalds, and get a raise.
I should have gotten into working on boat motors.