Check what tfp said. Also it sounds very lean and the idle is too high. If possible check with pressure and vacuum for any air leaks. And put on the deflector with cutter for the line, it is not good to use it without, it overloads the machine.
Another FS250 and FS120 owner here.....
A guard keeps the line from getting too long and causing the engine to bog during wind up. However the line length looks reasonable and shouldn't be causing the condition.
What I saw and heard was that trying to get the engine up to full speed the first time is difficult, with lots of bogging. Once you were able to get the engine up to speed once, the next up throttle cycle had just a hint of bogging.
I'd be checking the fuel lines first for cracks or a pin hole. To be safe, I'd just replace it. I had similar issues with my FS120 and replacing the fuel line corrected the problem.