Greetings! This is my first post. I am the proud owner of a 72 Delta 88 convertible. So, first issue. I have the factory q-jet on a 455. She starts fine and idles good until warm. Then she has a rough idle. What can be suspect here?

 

clogged gas filter(s)?

 

Welcome. When was the last time it was tuned? Post some pic's when you get a chance.

 

Has new distributor with Pertronix ignitor. New ac delco r45s plugs gapped .45. New carb base gasket. New fuel filter. New pcv valve. Idles good at cold start and gets rough after warm.

 

Is the choke opening fully when warm? Would run well cold then force you a little rich if not opening back up all the way.

 

Unfortunately, it could be a lot of things, some obvious, some not so much. Most likely is that the choke is not opening enough once the car is warm. Remove the air cleaner top and look at the carb. Once the engine is warm, the choke plate should be completely vertical. Other potential problems are a crack that opens as the engine warms up or a coil that is reacting to heat.

 

Sorry for the late response. So the choke does open fully, and when it does, it begins the rough idle. If I move the choke plate to a more closed position, it runs smoother. It seems not to respond to air mixture screws. I see no leaks after spraying carb cleaner. Car runs and drives but with ugly idle as if radical cam installed.

 

You've got a vacuum leak someplace. If closing the choke once the engine is warm makes it run better, it's getting air from someplace it shouldn't be. Check all vacuum hoses and connections. Check that the carb to manifold fasteners are tight.

 

I agree, sounds like a classic vacuum leak.

Also, you mentioned you gapped the plugs to 0.045".

If I recall, the spec. is for 0.035". The Pertronix replaces the points, but does not increase the voltage in the system - you're still going through your original coil.
0.045" won't cause your current problem, but it could cause a bit of rough running and will put unnecessary strain on your spark components.
I'd go back to 0.035"

- Eric

 

The '72 chassis service manual says the spark plug gap should be 0.040 inches.

 

I agree with Joe and MD, finding the vacuum leak is what you need to concentrate on....

 

Okay, so he's 0.005" high.

Thanks for checking and posting the right number, though.

- Eric

 

Look for that vacuum leak on what you fixed first. Carb cleaner will help you hear (not see) the leak. All new vacuum hoses are worth a few bucks if yours are original or old. Multiple lines can have multiple small cracks and you can go crazy trying to find the "one".