Help! - 1993 G20 Rebuild Won't Start

I am almost complete with a rebuild of my G20 Van. It is a 5.7L with TBI. I replaced the crank, camshaft, rings, had the heads rebuilt and now everything is back together. The engine will not start with both injectors plugged in. It floods out. If I unplug one of the injectors, it will run, but really crappy. It additionally is spitting some fuel back out the top. I have tried readjusting the valves which helped slightly but still won't run with both injectors. I have verified the timing at least to TDC. Should I replace the injectors? Am I missing something

Are you sure your at TDC on the Compression stroke? It sound like it's 180 out. When you put the dist in you can't just go by the timing mark on the crank, the mark lines up on the compression AND the exhaust stroke. The easiest and quickest way to verify is to pull the #1 sparkplug and have someone bump the starter while you hold a your finger or thumb in the hole. When you it reaches close to TDC on the compression stroke it will blow your finger out. Simply turn the crank forward or backward by hand to line up the timing mark and pop the dist cap and see where the rotors pointing. Also, are you sure you got the cam and crank timing marks aligned correctly when you installed the gears? Could be 180 off there...

I checked the TDC and it is dead on. I am pretty sure I got the cam timing correct. I found one loose valve and tighted it. It starts, as long as one of the injectors are unplugged but it runs really rough. If you plug in both injectors, it floods out. Could this be the valves too tight? I check all of the plugs and they are black. Could I have an injector problem.. I am running out of ideas.