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Took my 1967 Firebird 400 for emissions test. Failed for…

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Took my 1967 Firebird 400...
Took my 1967 Firebird 400 for emissions test.Failed for both HC PPM and CO%
Limits are 1000 HC PPM and 3.50 CO%What exactly is responsible for these values in a simple carburated car like this? Trying to understand what needs to be adjusted to correct the problem.
Submitted: 7 months ago.Category: Classic Car
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Answered in 8 minutes by:
11/27/2017
Classic Car Mechanic: Jaybird61, ASE Certified Master Technician replied 7 months ago
Jaybird61
Jaybird61, ASE Certified Master Technician
Category: Classic Car
Satisfied Customers: 2,312
Experience: Automotive Instructor at Palm Beach State College
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Hi, My name is Jay

Do you know if the carburetor is original or maybe a new one was installed that has oversized jets inside it? What was the readings your car put out to make it fail?

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Customer reply replied 7 months ago
The only thing not original is the carburetor. It is a Holley 600 CFM carburetor with electric chokeThe readings my car showed are:
HC PPM 293 AT 2500 RPM. HC PPM 2000 AT IDLE. LIMITS ARE HC PPM 1000
CO % 3.80 AT 2500 RPM. CO % 7.14 AT IDLE. LIMITS ARE 3.50
Customer reply replied 7 months ago
My car is otherwise all factory stock
Classic Car Mechanic: Jaybird61, ASE Certified Master Technician replied 7 months ago

Looking at these readings your engine runs good above idle but is too rich at idle. You can correct this by turning in both idle mixture screws and then may need to adjust idle speed up when the mixture screws are turned in. Also I would have the ignition timing checked to make sure it is correct. The basic carb adjustment should fix the problem.

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Customer reply replied 7 months ago
It's starting to get dark outside here, so I cannot go outside to make these adjustments now. That said, I will adjust the fuel/air mixture tomorrow using my vacuum gauge. After that I will check the timing and adjust it if it's off.
Classic Car Mechanic: Jaybird61, ASE Certified Master Technician replied 7 months ago

When you turn in the screws do one at a time and turn it in just until the vacuum starts to go down and then do the other one and do the same. This will ensure it is running lean enough at idle.

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Classic Car Mechanic: Jaybird61, ASE Certified Master Technician replied 7 months ago

My goal is to give you the best experience possible! I hope I have earned a 5 star rating! Please remember to rate my service by selecting the 5 stars at the top of the screen before you leave today. If you need more assistance, please use the reply box and let me know.

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Customer reply replied 7 months ago
I had already adjusted the fuel/air before I left Florida, but now I am thinking that having moved here to Colorado, with the cold weather as well as the altitude may be partly responsible for the rich condition. My understanding, how I have always adjusted fuel/air, is using the vacuum gauge and using small adjustments of 1/4 turn at a time, trying to obtain the highest vacuum reading possible and then once both screws have been adjusted, adjusting my idle back to factory specs. Do you concur?
Classic Car Mechanic: Jaybird61, ASE Certified Master Technician replied 7 months ago

I am in Florida and have lived in CO. You will need to lean out the mixture there. I do concur on your adjustment procedure.

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Customer reply replied 7 months ago
Jaybird, what do I have to do to close out the issue to get you paid? I want to ensure I can come back to touch base with you until I do the adjustments and get the car passing the test tomorrow.
Classic Car Mechanic: Jaybird61, ASE Certified Master Technician replied 7 months ago

Just put in a 5 star rating and i can close it out.

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Classic Car Mechanic: Jaybird61, ASE Certified Master Technician replied 7 months ago

Were you able to lean out the carb to get the vehicle to pass emmissions?

My goal is to give you the best experience possible! I hope I have earned a 5 star rating! Please remember to rate my service by selecting the 5 stars at the top of the screen before you leave today. If you need more assistance, please use the reply box and let me know.

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Customer reply replied 7 months ago
My car failed emissions a second time. I adjusted fuel/air properly but the results still failed me. I also adjusted the timing which was just a few degrees off.I took the car to Firest8who has told me that my carburetor has to be rejetted bec8of the huge altitude difference between Florida and Colorado.
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