Hey all.

This is my first time posting here, unfortunately it's because something is wrong, not because something is right

I just bought my dad's '83 F100 off him - he bought it brand new 23 years ago. It's got the 300ci motor with an auto trans. Anyway, the last few years I've been the one keeping it (somewhat) running, but unfortunately, I mostly know EFI stuff (from working on my old 86 mustang and my 04 SRT-4), so the carb is a whole new world for me...I can keep the thing running, just not very well. So I had the emissions tested today, and I must say...it failed. Here are the numbers:

HC: 3.09 (4.00 allowed)
CO: 128.41 (40.00 allowed)
NOX: 0.23 (5.50 allowed)

So basically I just failed on the CO part.

Anybody have some tips on things to adjust (and how) or check that could be causing the high CO output?

I wish I didn't replace the muffler for my dad a couple months ago (original was full of rust holes), I think that's part of what was keeping him passing, lol.

Any help would be appreciated.

Thanks,
Jason

 

First and easiest thing to check is to make certain that the choke plate is opening fully.

There is an idle mixture screw in the bottom of the carb. With the engine fully warmed up, turn that screw in until the engine starts to stumble, then back it out just a little until the engine smooths out.

If that doesn't do it for you, the next step is probably a carb overhaul. Pretty simple on those one barrel carbs, just make sure that you get the float level adjustment specs for your exact carb because they vary considerably.

 

The choke plate is the plate at the top of the carb, correct? I'm gonna have to go read a haynes manual for the truck tonight I think.

The carb is a fairly new reman unit from napa I think. That truck has had like 4 or 5 carbs on it through the years, we can only guess as to the original.

I'll try that adjustment tonight and see how it runs (it's a bit rough as is right now). Think this week I'll need to check out the vaccum lines and stuff...I know that some of the stuff on there is a bit...ghetto-rigged, for lack of a better term

thanks for the advice

 

hello,

Your Profile says you are from AZ. Your truck isn't a California import or anything is it?

Another good thing to do is change the oil, and do a complete tune up to the truck before you go get a smog check. Spark plugs, Cap Rotor, Air Oil Filters etc...

Check PCV valves... Check EGR valves, Catalyitic Converters, air pumps, thermactor air bypass and air diverter valves, ... if applicable...

The Cats can be checked with a Lazer thermometer. around 500 degrees going in, and 700 degrees going out, as example. Temp should be hotter going out the cat than in, etc...

hope this helps, and good luck.

 

Since CO was the only thing off [and way off], I'd guess the convertor is not doing its job. These things tend to run rich in stock trim which isn't good for the cat... builds up a layer of gunk on the honeycomb and it ceases to catalize much of anything. I've known people to wash them out with mineral spirits and go from fail to pass. It's a temp fix and just as much work as putting on a new one... only about $60 cheaper.

 

No, I don't think it's from CA, it was bought brand new here in Phoenix

The tune up it probably needs. I replaced the plugs, filter, and oil like 800 miles ago, but that was about a year ago (or more), so at least the oil is probably due. I was hoping I could get this thing passed and registered right away so my wife could drive it and then I could go through and fix the broken stuff, but looks like it's gotta be the other way around.

I don't have access to a thermometer like that unfortunately. Is there any other way to check the cat for functionality?

If I can get a replacement cat for $60, I think I'll just head that route. I wouldn't want to go through all that work and then have it still not pass That is a good idea though, I'll have to keep that in my head for future reference

Also, would using some Seafoam help any?

Thanks for the help guys.

 

As a general rule, high HC is an ignition fault. High CO is a rich condition. So the carb is the primary suspect here. Always a good idea to make sure the plugs are perfect since you said it runs rough, but since the HC is well within limits, run a compression test.

 

So here are the things that I've checked thus far:

-Choke plate is fully open when engine is warm
-adjusted idle mixture screw...it wasn't far out of adjustment, maybe 1 turn is all it took
-checked vacuum lines. Didn't see any cracked or broken, but you know those stupid plastic lines; I'll check again today.
-Pulled 1 spark plug, electrode looks good. Will pull them all and do a compression check today (if I can find my tester anyway)
-attempted to remove the cat. Stubborn pipes wouldn't allow. I'll take the air chisel to it todayto try and knock it loose.
-checked over and fiddled with the carb connections...here's where I have a few questions.

The solenoids on the carb (kickdown solenoids I think?) - The way they're hooked up doesn't look quite right, but it's the about the only way I can see them being hooked up. Is this correct? (See images)

http://synthetix.org/pics/truck/6-23-06/0606230053.jpg
http://synthetix.org/pics/truck/6-23-06/0606230054.jpg
(end result) http://synthetix.org/pics/truck/6-23-06/0606230030.jpg

The metal line that connects to the choke...Looks like it had been broken into 2 pieces and then electrical taped back together. I know that's not really the ideal thing, but is it going to make a difference from an emissions standpoint?

http://synthetix.org/pics/truck/6-23-06/0606230008.jpg

My Haynes manual says the choke plate should close when you open the throttle...it doesn't; what could be causing this?

I think that's it for now. I've gotta run to the parts store and get some misc stuff and hopefully get this thing properly working today. The wife had a work schedule change, so I have to get this truck licensed asap, or I'm stuck getting up at 3:30am to take her to work every day

Thanks

p.s. other pic's of the carb and connections can be found here: http://synthetix.org/pics/truck/6-23-06/

If someone has time to glance at them and let me know if anything looks not right, I'd appreciate it

 

The taped together pipe is the "choke stove" aka heat riser that supplied hot air to the choke thermostat, causing it to open as the engine warms up. Long as the tube is reasonably leak free it should be working, just check the choke cold and hot to make sure. You say the choke is fully open when hot... that shouldn't be a problem. The pipe gets pretty hot so electrical tape isn't a real fix, you can always bend up a new piece of copper or aluminum tubing to patch between the two ends of the break.

Wish I could help you with specifics on the solenoid hookup.. but my stock carb got pulled years ago and I never had to mess with them while it was on. One of the solenoids should be the fast idle solenoid connected to the throttle, electrically operated by the wire which also feeds the A/C compressor clutch. Not sure what the second one does...

 

Well I finally got time to go over it once more and get it purring smoothly. Just took it down, and it passed with flying colors. Here are the numbers:

HC: 0.83
CO: 16.89
NOX: 0.76


Makes me happy. I ended up replacing the cat, fixed a couple vacuum leaks, adjusted idle mixture, idle speed, replaced pcv valve, breather filter, air filter, plugs, cap, rotor...dumped some SeaFoam in the gas tank...I realized the last time the truck was filled up was in february! lol. (gas guage is broken, so mileage and dates are used instead) I wanted to check the timing, but I couldn't find the damn timing marks for some reason. It's pretty cramped in the front of that motor (I think it's just because of the fan...messing me up)

Thanks for the help guys.