I have a 1979 F-250 with 351M 2-barrel carb that failed Delaware emission inspection. The CO reading was over the limit. Does anyone know how I can lower this level? Does this mean I should lean out the carb a little bit?
Thanks!

 

Since it's a '79 does it still have all the smog equipment hooked up, i.e. Air pump etc.?

 

Make sure the air filter is very clean, retard the ignition timing 1-2 degrees max from OEM spec, add a bottle of "heet" (typically at Pep Boys) or Chevron "Ban-Ice" to the fuel (this is actually methanol- if you can't find these, try a local race shop- they should be able to get you 1 gallon of methanol (no more than 10% to the fuel!!!!). Assuming the fuel mixture screws are set correctly, lean out the mix by about 1/16 of a turn- you should be fine!

 

collinscd, fresh plugs, timing correct, new air filter, full tank premium gas oil change, & 1 i repeat 1 quart only 70% percent ISOPROPYL rubbing alcohol, common drug store variety, wel mixed and throughly mixed up and warm. get your crazy papers in order and get in line and go for it. you may be suprised. paul. end of advice

 

Thanks for everyone’s advice. The plugs were fresh last year and all smog equipment is still in place. I will check the air filter but I doubt it will be dirty. I only put a few thousand miles a year on the truck. I have heard about adding alcohol to the fuel system. I will try the retarding the timing a little bit and leaning out the mixture a tad.

 

Test your EGR valve operation. Unplug the vacuum hose leading to it, apply vacuum from a pump (or try to suck on it like a straw, if you don't have one! lol) and see if at idle it starts to run rough. If it doesn't, your EGR is stuck closed. You can try to clean it up by removing carbon from around the pintle and seat, and getting the diaphragm shaft to move in and out and possibly lubricating it with graphite or similar. The EGR valve should be removed to do this. If all else fails, replace it if you can't get it to work satisfactorily.
The EGR re-routes exhaust gases and reburns them, so it may help you pass. I am sorry you live in a place that does these tests on a 29 year-old truck!

 

hi collinscd, paul, i need to correct my statement, NOT 1 QUART, one pint, my fault, i was looking at the bottle as i typed. i am getting old. i make mistakes here and there. 1 pint is what i know works. how or why i cannot say young man. i just know its works for me.fair enough. i want to bring up MR trignot, please understand, he does NOT NEED paul to back him up or qualify him for ANYTHING. i know he is smart. my point, i THINKand/OR know his advice to you about the egr is ROCK solid, i can tell he has been there done that, why? because so have i, everything he said i have seen myself. they are problmatic and i say his advice is GOOD, do it it my be all you need. that pintle sob. i think a whole lot of the man myself, dont worry i dont need a priest its just what it is. carry on and GOOD LUCK as always later paul k. berwyn md.

 

I know I'm not being any help but I'm shur glad I live in canada!

Did it fail by much? Hopefully leaning out the mixture and retarding the timing will do it! Best of luck to you!

PS+ I'm just wondering, lets say you have an engine that you need to pass inspection, so you make the neccesary adjustments, (while losing power) and after it passes inspection, can you just re-adjust the engine to how you had if before to gain that power back? How often does it need to check out?

 

Yes you can "re-adjust" it after the fact,,, my 77 is due this year, I won't get started again on the whole BS SMOG **** crap,,,, chaffs my hide a bit. I am going to go fro a pre-test to see if it is close. If you find a good place, they will adjust it into spec, and ahem "inform you" of the changes they made, so you can correct it afterwards.

 

hi pick up man paul, i for one get it and i understand, carry on. bye me md.

 

I know this is an old thread, but we don't test in my state ,AR, but I have a dog box in my truck for hunting and the exhaust runs true dual strait back with glass backs, and my exhaust has a horrible raw smell and I am scared for the well being of my dogs. Will the air/fuel mixture fix my problem or will I have to add cats or something else more drastic? No smog equipped 77 f150 4x4 351m stock motorcraft carb, and oil bath filter (stock).

 

Running the pipes out the back may be the problem. There is a lot of swirling air behind the tailgate that might be sucking the fumes into the box. I had my pipes coming out the sides behind the wheels, and never smelled the exhaust. Might consider that. Clean, pretty much uninterrupted air moves along the sides of the truck to carry away noxious exhaust.

 

What was you CO at and NOX readings. I know when dealing with this stuff if co is high you need to move timing in one degree moves. If timing at 32 degree need to move to 31 or as needed. I do emmision testing on my industrial natural gas engines and 1degree moves can get me from 170 down into 145 nox. we use little different set up but still trying to get the majic number whatever that number is. Need more info on your paticular test, also how long of test. This is one of my favorite projects at work. Its challenging but its tuning of engines and what ever it takes to get it right. Need some more info on spec's please! On our test we do a 21 minute run on normal test. We have a few other tests but thats something else.

 

ive heard of one way that works, pour a bottle of 70% alcohol in the gas tank

 

My only option is the air fuel ratio or move exhaust because my state doesn't do test at all but my specs are 351m 4x4 77 no cats no smog stock intake oil bath air cleaner true dual exhaust and every thing stock except exhaust