1978 F150 400M-Pass Emissions?

[sbpbrent]

I recently purchased this old truck, and I need to pass emissions. There is no catalytic converter, and after researching a bit, the F150's didn't have cat's until MY 1979, but the F100's had them in 1976. The truck runs well, no smoke, and no gas smell in the exhaust after it gets warm. I've looked at a few threads here on the subject, and have come across very little. I'm looking for any advice, from inexpensive potential solutions, to more pricey options. I think I would prefer to keep the 400M and add a 4 bbl carb if I had to do something costly, rather than going to a 460 big block. It may pass, anyway. This thing was well maintained, with new plug wires, and new dual exhaust headers and glass packs. Any advice is welcome, and I am looking forward to interacting with some members. I've kind of lurked here for a while. Cheers!

[glc]

It should pass the way it is unless the carb needs adjustment. It should run lean enough with E10 gas. The only F150's that had cats in 1978 were California spec. What state are we dealing with?

[harrison28]

Another option would be to put smaller jets in the carburetor to lean it out.

[glc]

I doubt it would need lean jets - it's going to run lean with E10 to begin with. It's the idle mixture that may need to be adjusted. EDIT: I see you are in Colorado. For 1981 and older, the only testing is a 2 speed idle test. This should not be a problem if the idle mixture can be adjusted and the ignition system is correctly timed - and as long as the other emissions controls are present and functional. I don't remember what it may have, I know it has PCV, it may have EGR and air injection. There are also items relating to vacuum spark advance. Just take it out for a good run to warm it up and blow it out before you go to the testing station.

[sbpbrent]

Excellent glc, and thanks! Harrison, in Colorado it's 1975. It dovetails with something I found doing research on this: https://www.thoughtco.com/ford-f-ser...3-1979-3273774 The F100 got its cat's in MY '75. The F150's didn't get them until MY '79. Colorado categorizes '78 and older trucks having a Gross Vehicle Weight Rating (GVWR) of >6100# as "Heavy Duty". '79 and later it's >8500#. Thanks for the replies!

[sbpbrent]

I don't think my last post stayed up, but many thanks glc and Harrison. This is an interesting read about cat's in the Ford F series 1973 - 1979: https://www.thoughtco.com/ford-f-ser...3-1979-3273774

[glc]

The federal break point from 75 to 78 was 6000# GVWR. There were some vehicles less than 6000# that complied with 49 state emissions without cats, most were 4 banger Japanese compact cars and trucks. California required cats on everything starting in 75. 79 and later was cats on everything except some vehicles over 8500# GVWR till 81, starting in 82 everything had cats. My neighbor had a 81 Chevy 1 ton crew cab pickup with a 454 with no cats, but it did have a smog pump. He had a heck of a time getting it past the Illinois inspection without the cats, it took him months to prove to the morons at the state that it never had them. You know, the F-150 was originally created in 75 for the express reason to avoid cats. They beefed up a F-100 just enough to get the GVWR over 6000#. Chevy did the same thing with the C-10, they called it the "Big 10".

[sbpbrent]

Update: It passed emissions easily. I guess I shouldn't have worried about it so much. Now, for the stereo....