Hi Aug...
Three? Hmmm...there should be a High speed, a Low speed, and the idle r.p.m. adjustment stop screw which is also the carb barrel retaining screw.
The Hi and Low are the only ones you really need to concentrate on, for now...
I would set the high speed at around 3.5 to maybe 4 turns out...

Setting the low speed can be tricky if you don't have a baseline setting. The low speed is the one that's in the center of the carb arm.
While looking down the barrel of the carb, adjust the low speed until the tip of the needle till it's about 1/32" away from the spray bar (or fuel inlet tube ) at Wide Open Throttle (WOT )

Just had a thought...
Tower had engines made by O.S. and I think MDS, so there might be some differences.
The O.S. engines might have an air bleed carb?

Can you post a picture?