problems staying started...

I had my engine rebuilt and it was running just fine till yesterday, all of a sudden my truck didn't wanna stay started..it starts but then it revs real high then dies...I need suggestions why it does that. Could it be my timing, carb(Weber)?....please help

First: how long ago was the engine rebuilt and then running OK?

Did a local mechanic rebuild/install this, or did you buy a renuilt engine and install it yourself?

Should we assume that the truck is a B2000 or B2200, and not a carbureted B2600?

Yes it was a local machine shop who rebuilt it. It's a 86 b2200 carb(Weber). And my truck was doing just fine I barely put 700 miles on it...

Sounds like it's starving for fuel, the way it revs up right before it dies.

Well that was part of the problem. I had to take my whole carb off and seal the gaskets on better..but now it's running just fine.

Gaskets sealing and the need to sand the Weber adapters flat is a HUGE issue with the Weber carbs. This cannot be over-emphasized !!!