You say it will start when you push it? Sounds like an ignition problem, related to the battery voltage drooping while cranking.
Or what a lot of people (myself included) have experienced is the fuel boiling in the float bowls and jets, pushing fuel out into the intake manifold and causing a very rich condition. This typically shows up after driving fairly hard (like uphill or freeway speeds) followed by immediately shutting the engine off for 5 to 20 minutes or so. On a club run a few miles back, after we stopped for a "biology break" in the mountains, there were quite a few of us that almost couldn't get them started again. I can't explain why, but it seems to have gotten much worse with ethanol in the fuel.
In my case, adding a heat shield under the carbs made a big improvement, although it still runs a little rough at first under those conditions.
Another thing that seems to help is to follow the book suggestion and hold the throttle partway down while cranking when hot. I think it helps move more air through the carbs & manifold, to clear out the excess fuel.
Here's a shot of the heat shield as I was installing it.