NEAL1940

My BR 380 starts after being chocked but bogs down when reved up. Have changed spark plug, fuel filter, and rebuilt carburetor. When I bypass fuel line in tank and put fuel filter on end of carb input line and drop it down into tank, unit starts and will rev up. Have checked the fuel line in tank, can not find breaks or blockages. Can the flexible tank fuel line be collapsing under vacuum from carb.

Ok so lets think this out. If the fuel flows freely through a fuel line then the line can not collapse from vacuum. If something is blocking fuel from flowing freely then vacuum could cause collapse if it was strong enough and had enough fuel to run long enough to create such vacuum. I don't think it is possible to collapse the fuel line but I bet it is clogged somewhere so it can't suck fuel fast enough.
By the way you already figured out how to fix it. Replace the fuel lines.

And if the arb has a primer bulb with a duc bill valve in it they can fail and give a similar set of symptioms.
In the shop we pressure & vacuum test fuel lines, tanks filters & carbs.
However if you ain't got the gear, just swap the fuel lines & filter.
Doing so is cheap and will not damage the blower.