It runs like a beast for 25 seconds, and then dies. I can't figure it out.

Carb'd? EFI? Provide some details. More than likely you're running out of fuel. (ie. fuel bowl runs empty.) You'll need to find out if you're loosing fuel or loosing spark.

I think I'm losing fuel. I readjusted the timing, it has a new edelbrock carb that's been tuned, and a new distributor and cap. When you crank it it takes a few revolutions and then lights right up, runs like normal either idle or under load, then dies. It dies the same way every time. It doesn't have a choke.

That carb is tuned to what? Not your engine, it hasn't ran long enough to tune. But that's neither here nor there at this point.

I'm going out on a limb with this guess. If you need to crank it a bit long to start and then it only runs briefly, you're needing to crank it to fill the fuel bowl and the pump doesn't keep up afterwards. Possible lack of supply to the pump or from the pump. Pinched/clogged line? Weak/bad pump? Check fuel pressure to the carb.

It's a carb and no choke... Are you warming the thing up 1st. Like say crank it and hold throttle so it runs at 1200-1500 rpm for a min or two, rev it up a few times, etc...

Or are you just cranking it up, letting it idle then it dies?

It's gonna have to warm up, and RPM will have to be increased during that time (that's what a choke does).

If you are warming it up and it's dies out then you are not getting fuel to your engine.
Could be a dirty carb, clogged up filter or line, bad or weak fuel pump