We live in a row home, built about 60 years ago. The pressure on the
2nd floor isn't the greatest due to the small (in diameter I believe)
copper pipes they installed when the house was first built. The
pressure isn't bad, you just don't get a real powerful flush.

Our previous plumber said it might be the... "flap"... I believe?

I don't think it's the ball and chain in the tank, that's just to keep
the toilet from always running and sets the level for the amount of
water to flush with (from what I know).

So is this an easy DIY job?

I'm wondering if the reason the toilet flushes 2 to 3 times is because
the pressure isn't so great, that any.. um.. "leftovers" that didn't
get flushed initially should be the 2nd, 3rd time around. But this
can't be true, i grew up in a row home and never experienced this, and
never experienced this really, ever.

Thanks