Hello, my 79 250 I6 starts easily, but runs rough until it is warm, and seems to lack the power it should have. When shifting, I am hearing popping (but not a true back-fire). Upon shut-off, it “diesels” a bit (engine chugging while the key is off).
This engine has vacuum lines running everywhere, and I replaced obvious cracked and broken vacuum lines, checked the PCV valve (it is ok). The exhaust smells like all the fuel isn’t burning.
Any thoughts on the next steps? I thought about new plugs and wires. It has 67k miles on it.

Thanks in advance.

KSBandman

 

What gas are you using, ethanol, etc.?

 

 

Since you said it diesels when shut off, an engine/carb that old might not like what gas you are using. That would be the first thing I would look into. Rough idle might be something different, and I agree with replacing vacuum lines.

 

 

You might try a different heat range spark plug if you cannot up the octane on the gas, what part of Kansas?

 

 

Check for the proper operation of the choke and related items. Also check the timing of the engine.

 

 

What plugs are in it now, and are these the same direct replacement? Does the idle change with air temp, and as suggested by oldchevy, when cold, is the choke plate closed?