Fuel delivery problem. A small leak in the fuel line between the engine and the tank will take in air and cause this. So will something plugging up the fuel filter, or the pickup screen in the tank. A common problem is a loose or leaky pickup tube in the tank. If the fuel pump hasn't been serviced, that's suspect.
If the primer bulb sucks flat, it's a plugged screen. All the rest of the problems will just result in a bog.
DO NOT TRY TO RUN IT LIKE THAT. Just before it bogs, it's at about the right mixture to burn a piston.
Troubleshooting tricks. A piece of clear hose spliced into the fuel line to see any air getting in. A pressure gauge (15 lb) put in the fuel system. Should read 2 - 6 lbs at all times the engine is running. Each carb has 2 pipe threaded holes on the fuel rail. One is left with a plug in it, usually the lowest starboard one. Replace that with a nipple and hook up a temporary pressure gauge.
BTW, if you title your thread with something identifying the engine and trouble, like "V6 150 bogs at WOT", you will get more help.
hope it helps
John
