273 intake on a 318

I would be amazed if you found anything in the intake runner. the engine running would have sucked anything in a runner that wasn't really really stuck in there. my guess is, it's in the carburetor. did you do anything inside it? if the jets are too lean the farthest cylinders from the carb will starve. this would be exaggerated if one side were plugged up. I would go through the carb if you haven't already.