300 wont stay running
 

I have a 1979 block that I put in my 83 ford. I bolted the exhaust manifold and air intake manifold from the 83 motor and put it on the 79 block. My question is is that why wont it stay running? It starts up, then revs really high then dies. but when I step on the gas to keep it from dieing it revs high still and wont idle. Anyone have any ideals.

Vacuum leak

Clogged idle air passage in the carb

How would you check to see if the is a vacum leak?
For the clogged idle air passage in the carb, could i use some carb cleaner to fix that problem. Thanks for the ideals.

Double check that there are no open ports on the vacuum tree off the intake manifold or the carb itself. Re-check the carb mounting nuts are tight and the base gasket is intact. Did you use a new set of gaskets for the manifolds and tighten them in sequence per the manual? If everything is as it should be, then get yourself a vacuum gauge. One of the handiest automotive tools I ever bought.

Clearing the idle air passage would probably require a carb rebuild. Your symptoms sound like what happened to my 302 after I ran some bad gas - it would run at fast idle until it came up to temp and the choke opened then die. The low speed circuits were all gummed up. Runs like a charm now after a carb rebuild.