Hmmnnn, try and drop it(the speed) down to about 6.. Then, try that tuning method I advised.. It's easier with the flow turned up, but from what brs told me about my 203, the motors can be a bit too powerful, therefore not taking a good bite out of three water.. And I don't know the depth of the 143, but usually, for the phrase I've had(given, they are larger models), but they always said 8.5 to 9.5 inches..
But, I would try the adjustment with the air control valve first.. With the gate all the way open.. And you will see the water start to rise.. Then, just back off the air valve a little.. Then, start closing your gate valve.. And at that point, you may have to turn the speed up, maybe not..
But it looks to me(from your video) like, it's trying to build foam, but maybe either it's too low(water level in the body), so foam production is slow, or it's just maybe going through too fast.. But I err on too low as far as the water and bubble level..
And the venturi he was talking about was the air line interface.. Where you attach the air hose.. Sometimes those clog, reducing the amount of air that can be ingested.. Have you checked that to make sure it's good and round and unclogged on the inside?