Hey all. every year my truck fails the HC part of the emissions test. I always retard the timing and it passes great. This year the HC are fine but the CO levels are way off both at idle and high speed (2000 rpm) I need some ideas of what I can do to fix it quickly, the damn thing expires today and I want to keep driving my truck.

 

I'd check into a sticking choke, clogged air filter, fuel bowl running over.

 

Need to lean out the carburetor, either thru the idle mixture screws or jets.

My procedure back in the day was to lean out the screws as much as possible while trying to keep the engine running. Install some slightly smaller jets as well.

Set the timing to factory specs as well.

HC and CO went way down doing that stuff, but NoX went sky high, fortunately they didn't consider that in their testing.

But, if yours suddenly went up, I would check the things that was mentioned, air filter, dirty carb, choke opening, spark plugs and ignition condition.

Josh

 

Thanks for the help. Just checked the carb, (ok) put in a new air filter, plus plugs, wires, cap, and rotor. Adjusted the timing a bit, I am off to try again.

 

well, still failed, better but co is way off. This carb is dumping to much fuel. Mabye I will pull the motorcraft carb of my cj5 and slap it on for the test.

 

Isn't the Thermactor system (air pump, bypass valve, hoses, idle vacuum valve, and check valve) responsible for reducing co emissions? I read it in my Haynes manual, but have no earthly idea where/what it is...no pic. My manual is for 73-79, but I don't know if all engines had this.

 

My F150 did not come with a air pump or anything. just a egr valve (which I broke down and hooked back up)

 

What kind of carb is on it now??

 

it is a barry grant Demon 500cfm 2 barrel. I am thinking of just dropping a few jet sizes and checking again.

 

OK I have some questions on jet sizes. The I/m limit is 3.00 on the co, my truck is putting out 7.03 How many jet sizes should I drop?? On the idle side the limit is also 3.00 I am at 5.83 I am assuming I can just lean out the mixture screws to bring the idle into specs? I think my jets are #75 (hole size is .0820) right now. It came with #78 jets in it and I dropped it 3 sizes because I live at around 4500 feet.

 

I'd go to somewhere between a 70 and a 72 that should get it down to a level manageable by the mixture screws

 

Thanks!!, I guess I will head to checker sunday and get a couple differant sizes. I am kinda looking forward to getting everything dialed in, but scared at the same time, Damn truck runs great now. I just got back from Idaho last week on vacation and she did 600 or so miles without a hiccup and got almost 11 miles to the gallon.

 

You should get better mileage even after changing jet's...it won't be consuming quite so much fuel...it's basically wasting some as unburned..too rich

 

Change the engine oil and fliter as well.

 

Yea probably a good Idea.