I just rebuilt a flathead, stuck it in, and it fires up beautifully, only it won't idle. I double checked timing, advance is working, carb has been rebuilt, actually by me after I thought that was the problem but it does the exact same thing.

The idle speed screw is all the way, the mixture screws are one turn out, and when I pull the wiper hose off it idles great, so it seems to be not getting enough air. I rebuilt the carb because I thought that it some dirt or something in it, but it acts the same way. Are the throttle plates supposed to be at least a little open? Mine seem to be shut tight....

 

The buttlerflys should be open just a crack.. otherwise it isn't sucking anything in. Your choke plate should also be wide open when it isn't running.

 

if you pull off the wiper vac. and it idles it would most likly be a vacume leak

 

pulling the wiper vac creates a vacuum leak!