Engines can get air from the exhaust. Its a long story so I wont explain it. It also comes from the circumference of the blades.
Watching the video the engine looks as though it has a stammer or some rough running cylinders that's causing the shaking. What's IFR and IAB in that carb?
I pulled two plugs tonight to do a compression test. Both plugs looked extremely clean. Light brown I'd say. I got tired at the end of the night but number 1 and 2 are at 145 psi. I will do the rest this weekend.
