I failed emissions. Could use advise on what to do. Retard timing? Pour denatured alcohol in tank? turn mixture screws in all the way and then out by how much? -Thank you

 

HC is unburned fuel. .. it's running rich.

Every vehicle is different so telling you how many times to turn the mixture screws would be useless.

Go back to basics and perform a tune up... with a timing light, vacuum gauge, attention to detail, and patience.

 

You have to sniff a 68, wow.


He's right you're rich, what to do depends on your understanding, what you are up to, if your next test is free etc. There is a good chance that just leaning out the idle mixture will get you to pass. But if you fail what are the consequences, does it need a tune up anyway, etc.


If you decide to lean it out with mixture screws here's what I suggest. Grab the tools you need to lean out the idle mixture and toss them in the truck. Drive to the testing place and just before you get there find a place to stop and mess with it. You'll want it warned up and run hard before hand, and you're gunna make it run like crap. Turn each screw in just to the point where it starts to slow under test conditions, that is if they test in gear adjust in gear. After you pass, stop again and adjust it back.

 

It could also be running too lean.

I agree that a basic tuning is needed. Your carb may also need to be rebuilt.

Where are you in the state gertie? I or others might be able to come help you.

 

Here in Arizona if the you fail the first emissions, the retest is free. If you fail that, then you start at the beginning and have to pay full price again.

 

In California the test cost is around $40.00, oh I forgot, my 68 doesn't need to have a smog test!!! Sorry just a little ribbing. Like others said, give your baby a tune up and try adjusting that carb using a vacume gauge to properly set that carb.

 

I'll just add that a base A/F mixture setting after a carb rebuild is 2.5 turns out.

 

my problem was waaayyy rich and smoking. replaced valve seals and solved problem

otherwise you need smaller jets

 

My problem that started my whole fiasco a year and a half ago was a lean mixture. I had the same problem with HC's. But my CO levels were way below the limit. If it is smoking black then it is way too rich. Your power valve might be stuck open?

I would set timing to around 12*. Idle screws to around 2 turns rich, and idle speed to around 800rpm. ( you really need a vacuum gauge to do all this properly)

 

CO's are what the carb's putting out and HC's are how well the engine is burning it. I have not heard the engine run but 1st I'd do a compression test on it. If the engine is worn out enough nothing will help it pass emissions. If all cylinders come back within 10% to 15% of each other and at numbers that make sense a COMPLETE tune up and carb overhaul are in order. Plus you'll get better gas mileage. Win-win situation.

 

Wow there is a lot of misinformation here.


HIO Silver you have nothing to base this on nor could it be in any way correct, it's only misleading to those that don't understand. You have no idea what carb he has and base settings are only to get it started to make adjustments, after an engine will start base settings like this are pointless. Nor is 2.5 a good base setting for any carb that comes to mind.


What you said earlier was correct.
High HC and low CO would indicate a miss. HC is unburnt fuel, CO is incompletely burnt fuel. It's possible to have both high or only CO high due to being overly rich but if only HC is high then it's a miss. A miss could be caused by being lean but is most likely an ignition issue.


Blown PV is possible, unlikely and pre-mature. Test is to turn the idle mixture adjustment screws in far enough to stall the engine. If you can not stall the engine by turning in mixture screws then a blown PV is likely, assuming a carb with a PV. For example Edelbrocks don't have a PV, in the case of an Edelbrock it would indicate a high float level, which is still a possibility on a carb with a PV.


Suggesting timing at 12 and idle at 2 turns makes no sense. There is no way you can know that that 12 is appropriate for the OPs engine and idle mixture as I said above idle mixture as turns out is only good for base settings before the engine is running.


Yes a vacuum gauge is a good thing to have for adjustments, but the same can be accomplished with a decent ear or accurate tach.

Huh? CO's are what the carb is putting out, this makes no sense.


Put simply fuel is a molecule made up of a chain of Hydrocarbons(HCs). The engine combines in the right amounts and combusts the HCs with the right amount of O2. Ideally HCs and O2(atmospheric oxygen) break up and recombine to produce H2O(water) and CO2(carbon dioxide). Excess CO(carbon monoxide) is produced when there isn't enough available O2, lean. Excess HC is produced when either there isn't enough O2 or if combustion wasn't either initiated or complete enough to get what HC and O2 there was to combust.


I'm not going to say a compression test is a bad idea, always a good thing to know. But it is pre-mature in a process to solve the problem. There's no indications of a compression issue.

 

I disagree brute. I think there's a lot of good info here...

2 turns is a good starting point since 99% of carbs have a useable range of about 4 turns. And 2 turns will make almost everything run. Although this is just a base setting and is probably not tuned correctly. But it gives the OP a good starting spot. 12 degrees timing is the same way. It's probably not perfect, but in my experience, most of these old fords run pretty good at 12. Just a starting point. I run mine at about 14. My problem was a misfire, from a lean condition. But I only figured that out much later.

 

But the engine is already running, base settings lake that are only just that base settings. They do the OP no good and someone might get the idea that he should go back to those base settings he SHOULD NOT. So then what is the point of bringing it up? All posts like this do is clog the thread with poor advice and misinformation that does the OP no good.

 

He asked where to set everything. We don't know what it is at now. So were suggesting the baseline.

 

The first two points are true, what is also true is that the OP hasn't given us much information nor replied even though he was logged in for some time. That we know very little makes it very hard to give specific advice. Still though it's not correct to suggest a setting to a baseline. Better to explain that these settings can't be adjusted over the internet, no number of turns will be correct. What is correct is to explain how HE must adjust it based on how HIS engine responds.