Cycling... My Legs Run Out Of Energy Before My Cardiovascular Does

1. More cycling

2. Make sure you are eating enough, although you don't really need that much for a 2h ride.

my legs ache too, but i can still go a bit faster, or at least not slow down.  i've learned that they just don't hurt any (much) more when you keep pushing.  it's what happens when you ride hard.

ride loads and 1. they'll ache less and later and 2. you'll get used to it.

"Ride Lots"

I've also found that Accelerade (4:1 carbs/protein) Sports drink is the stuff of miracles.

As well as ride more, slow down on the longer days so you can go for a longer time.

It will come with time.

It's not just longer, but a matter of volume as well. Is a two-hour ride normal for you, or is it an anomaly? If you're not regularly doing rides of this length, then of course it's going to be hard on the legs.

Your logs don't appear to be complete, so not enough to go on there...

If you haven't already done so-Get a proper bike fitting.

I had the same problem, except I've been riding for quite some time.  At my fitting, we determined my chronic  tight hamstrings were causing my to pedal 'toe down'-It's almost impossible to go any distance (and still have power) in this position.  After we changed my position-Whola!  No fatique and more power.  Oh, and Ride More!