Hello everyone and thanks in advance for any help. Been fighting with my local Emissions facilities with my truck since November of 2017. First off, I inherited this vehicle from my uncle when he passed away last September and he lived in an emissions exempt county so he had changed several things on the truck and I've been spending lots of money and countless hours changing/adding things to the truck to get it to pass. I've been getting the run around from my emissions facilities here on the required/non required components. I finally got a straight answer on what I needed to add/change to pass the visual inspection after having to have a state inspector look it over. Here is the background of the vehicle.

The Truck: 1979 Ford F250 Single cab, 8ft bed, Camper Special, 4x4, 6.6Lt 400CID engine, manual trans, 8100GVWR

Changes made by uncle (that i know of):
Suspension: Detroit lockers front and rear, 4in or 6in lift (not sure which) with 35x12.50R16.5 tires
Engine: Custom true dual exhaust with flowmaster mufflers, Edelbrock 750CFM 4bbl Performer carb, 351C 4v exhaust manifolds, 351C 4v Cylinder heads, Edelbrock 351C 4v performer intake, Holley adapter kit to install 351C intake onto the 400cid, edelbrock mechanical fuel pump, removed cat converter, unhooked air pump, mild street/strip cam, MSD 6AL controller, MSD distributor with mechanical (weighted) advance, pistons were changed when engine was rebuilt it 1996 but not sure what style pistons were put in, carb had .104 main jets with 070x037 metering rods and .107 secondary jets with 8HG step up springs. I think that is all.

Changes that I've made to appease the emissions people:
Suspension: None
Engine: Convert to single exhaust, add a Magnaflow cat converter (still using the Flowmaster muffler), Edelbrock performer intake for the 400cid, hook air pump back up (had to gut the air pump since the 351C heads do not have the passage cast into them for the air system), spark plugs, fuel filter, timing set about 3 degrees advanced from stock setting, oil change.

I took it to get emissions after those changes and this was the result:
HC PPM: 2500 RPM = 523.1, Idle = 766.6, Limit = 400
CO%: 2500 RPM = 8.02, Idle =6.84, Limit 1.50

After that test I changed the the metering rods to 070x042, changed secondary jets to .104, put 3HG step up springs in, disconnected the secondary linkage to prevent them from opening during the test, put idle mixture screws at 1 1/4 turns out from fully closed and was pulling 15.8-16 HG's here at an elevation of 5,344ft.
I then took it back for my free retest and this was the result:
HC PPM: 2500 RPM = 347.2, Idle = 498.2, Limits = 400
CO%: 2500 RPM = 7.82, Idle = 5.86, Limit 1.50

I am now at a bit of a loss. The only thing I can think of to do is to change the jets and rods again to the next stage lean, per the edelbrock owners manual and turn the idle screws in about another 1/2 turn. Does anyone think this will do the trick or have any other suggestions I can try? Thank you all for the help and taking the time to read my post. I apologize for making so long but wanted to make sure everyone here had as much info as possible. And again. thank you all for the help.

 

750 is a pretty big carb - you might not be able to get it tuned down enough at idle, heard of that before, I believe... All your symptoms point at running rich at idle. I've never seen it done, but is there a set of manifolds that allows an external air pipe to be added, Chevy style? Other thing can be it's choked down - what do you have for an air cleaner? Some "performance" 'cleaners are worse than stock.

Any idea what the actual engine temp is? You might need a hotter thermostat, that can help.

I'd mount up a wideband A/F sensor and play with it some - you occasionally have to make it run worse to get it to pass.........

 

More info is usually better than too little, so off to a good start I'd say.
Welcome to Ford-Trucks.com too by the way.

Not sure if it's a rich-lean issue, but you could try using a controlled vacuum leak of some kind. I've done it with using the wrong PCV valve for my 302 when I'd go to higher altitudes. I'm at sea-level normally, so when I go up to 8000' it's pretty rich. The PCV valve letting too much air in was a great semi-cure.
Was too lean for good running down low though, as it would stumble off-idle and did not have full power.

That said, did they comment on the ignition timing being too advanced? Normally here in CA they actually go by the book on that and want you to set it exactly at what the factory did. If your area does not do that (you're already getting away with a 4bbl carb after all) then maybe you can try advancing or retarding the timing.
I would base which way on what others here have to say that have more knowledge about that kind of thing though. I'm only guessing, and you don't want to make more work for yourself and upset the "free return inspection" guy by not paying them.

What about the ignition itself? Have you tuned it up lately with new plugs and wires and such? Maybe the old coil is a bit soft from old age? Just wondering if some more sparkage would help things.
Thermostat? If it's not reaching at least the full 180 degrees, you're fighting an uphill battle right from the start. Better still would be a 195 just to hedge your bets a little.
Do you warm it up fully by driving around for awhile? You using regular gas instead of premium?
Just a few things to think about. Hopefully someone has more insight for you than I could come up with.

And while there is a better way to check for vacuum leaks than what you described, I would think some leaning out would be good. But if it's uncontrolled and only in a single cylinder or one bank of the engine, that would increase emissions.
The better way would be to spray some brake cleaner around the engine while it's running. If you spray right on to tubes, gaskets and fittings and the idle changes at all, then you've found a leak. Most of which you won't find simply by blowing/sucking on the hoses unfortunately.
Or fortunately actually. Since spraying is easier than just about anything else. You can even use a spray bottle of water if you're nervous about flammable liquids (that are not actually all that flammable in the real world) flying around your engine compartment.
Just keep the spray off of any newly painted surfaces. Old paint is ok, but new paint won't like it.

Anyway, good luck with that.

Paul

 

What Jake said about the size of the carb. If your engine is otherwise stock (cam and stuff like that) then even a 500 carb would not be out of line. But a 650 would be a good medium.
Edelbrock carbs, based off the old Carter AFB, are actually pretty tunable and forgiving of over-sizing. But 750 is still pretty far at the high end of acceptable.

Paul

 

I have a 77 400 with 8.8:1 compression . Im running the 600 cfm. I dont know how wild the motor is in yours , but here is what one site has to say.

"

 

Cool resource Bulldog. Did you archive that site location, or can you search it and have something come up? Since it's a closed site, even clicking on the upper logo just sends you to a "site suspended" page. But if it's generally available it'd be nice to know the path to it.

Used to be one of my main hangouts online back in the day. Now most of us are spread out all over the place it seems.

Thanks

 

Jakehan - It was the factory air cleaner housing on it but i have a standard air filter that is about twice as tall as the factory filter. I'm not sure on engine temp. I have not had a chance to put a infrared thermometer on it but I believe it has the standard 180 degree t-stat in it.

1TonBasecamp - thanks for the welcome. Here in CO they do not check anything like that. They do a quick visual inspection to make sure the vehicle has the correct amount of cat converters, that the air pump is hooked up, has the correct amount of O2 sensors, has a gas cap/is in good shape and they check for the CEL. they don't look to see if it has an EGR on it, which mine does not, nor does it have the thermatic parts on it. I did forget to mention in my first post that that i did change the plugs (gapped to smallest side of spec), put new plugs wires on and did put a new MSD coil on it. I do get it fully warm at the house then drive it at high revs the 15 miles to the test center and when i get to the test center, I keep the revs up while waiting in line to try and keep everything as hot as possible for the test. I have been running mid grade gas in it (here that is 87) cause i can't justify the cost of premium (91 here).
I do agree with you all that the 750 carb that's on there is probably to big but I don't really have the money to go out and buy another $400 carb and $60 calibration kit. I was able to pick up some smaller jets and larger (fatter) rods to put in it to lean it out more, just didn't know if that would do it. I've been told that if its close to passing a "trick" to try is to put a couple gallons of E85 in the gas tank mixed with normal gasoline and that will lean it out enough to pass it. I think that wont work though because i think it is more of a A/F ratio than anything else. I just know very little about carbs. All my knowledge on them is self taught. Thanks for all the comments.

 

Ah, Colorado - the fun of dealing with the front-range. Get a post office box in Alamosa and register it down there, they don't test.

Seriously, though -

Another idle trick is to set it up 50 RPM on the linkage, then pull it back down where it's supposed to be with the mix screws - "lean idle drop", I believe is the term. I've always set them lean high, I think it runs better, but nothing says you can't necessarily re-tune.... At any rate, I'd also get a gauge on it, they're not all that expensive anymore.

Avgas can help with the CO, too, I believe, burns hotter. Used to do it every once in a while on old truck motors just to clean them up.

And you should be fine on air, would seem like, but you might also try tying the hot air flap closed so it's pulling air off the manifold.

 

I don't have to have inspections, but it seems to me that everything on that engine is going to make dirty exhaust.
No air injection, no EGR, 4V Cleveland heads (huge intake runners), big carb, aftermarket cam.

Good luck.

Emission testing, emission failures and repairs.

 

Yes the logo in upper left is suspended , but I clicked on the upper right back button and it works

 

With those numbers, that truck is running like crap, dumping fuel. I mean 8.0 at idle on Co, good lord that's practically gas running out the tailpipe. I've had stock trucks older than that idling in the .10 range. You have more going on than just changing jets and needles.

 

1979 F250 X2 on welcome to FTE, lots of smart folks on here that also deal with that emissions stuff and they should get you squared. Thankfully I do not have to deal with any of that in my state.

1tonbase ProjectBronco.COM! A 78-79 Ford Bronco Resource Center and go to the L/H side of the home page a scroll a few down to the "technical" link. BAM

 

I can't say from personal experience, but these are some things I have been told for beating emissions.

1) Retard timing.

2) Lean out the carb....changing jets without looking at the color of the spark plugs after a test drive after the change is like a blind man trying to read a book. Plenty of good info online if you look about how plugs are to look.

3) Only after the jets are dialed in right can you adjust the idle screws...while this can be done by idle speed a vacuum gauge is the best.

4) Make sure you don't have any vacuum leaks.

 

Between the 750 carb, Cleveland 4 bbl heads, and the cam, I don't know if you can ever get it down where it needs to be.

I owned a 351 Cleveland 4 bbl way back in the day when it was practically new. All stock, the exhaust would burn your eyes coming out the tail pipes.

 

Wow. I totally missed the big-Cleveland add-ons. Yikes!
Yes, like the others have said, you're going to likely have to do some very fancy footwork to get some 4v Cleveland heads to burn clean.

Maybe it can be done, but I'm not sure how to get there.

Paul