Your problem sounds exactly like mine, I have a 50 3800 with a 1966 250 in it. I rebuilt the engine years ago and it never ran because of that problem. It kind of was put on hold for a number of years til now and I have been going at it hard. Everyone said it was a vacuum leak but that wasn't the case. With help from this web site I started with the basics and did the points , condenser, timing etc. I got it to idle finally without being choked but it still had zero power when I tried to drive it. An old timer said your carb needs to be rebuilt. ( It was a new rebuilt Rochester Monojet) I took it off, got a new carb kit and delivered it to him. Today I was all excited and put her on, fired her up and had gas pumping out everywhere. Upon inspection, he had cross threaded the fuel inlet fitting so bad that the carb is shot. He also removed some plug in the carb body and gas poured from there as well. Now I guess I need to find another carb, And back to square one. Good lick on your project and I havent read all the threads but someone may have told you this already but start with a basic tuneup and leave the carb to last. I will try to find the info that was sent to me and I will forward it along.
