Emissions Test
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Joined: Apr 2005
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Emissions Test
I have a 68 F100 with a 390 and a 2 barrel carb. I recently had to have the emissions tested, and unfortunately failed the test. My Carbon Monoxide output was to high. Any ideas what I can do to fix this? I recently rebuilt the carburetor. Would having the mixture set wrong cause this to fail? Would fuel additives possibly cause problems? Any hints, tips or advice would be very much apprecited!
Post Fiend
Joined: Jan 2003
Posts: 8,600
Likes: 4
From: Iowa
Lean it out, that should fix it. If it fails at idle, lean it out a little there, if at speed stick some smaller jets in it.
On another note:
Since when does a 1968 truck have to get emissions testing??? That's rediculous, do some research on your laws.
On another note:
Since when does a 1968 truck have to get emissions testing??? That's rediculous, do some research on your laws.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
I now live in an unincorperated town on Hood Canal with a view of the Olympic Mountains and Hood Canal out the front windows. I can hunt in my backyard (Deer, Bear and Elk in the western part of the county) and fish in my front yard along with crabs, clams, oysters and shrimp. Ride my quad from the house into 4000 acres and over 200 miles of roads and trails. And no emissions test at all.
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Fleet Mechanic
Joined: May 2004
Posts: 1,436
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From: Montana
I cant stand emissions tests... In california were at i think 74 or 76...right in there is the cut off.
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Postmaster
Joined: Nov 2002
Posts: 3,447
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From: Littleton, CO
Originally Posted by Bear 45/70
Do like I did, when the 428CJ wouldn't pass anymore, I moved to where there is no testing. My stress level dropped by 75 percent also.
Here in Colorado, the pre-1981 cars are tested differently, but you still need it for plates. On the "classics", you can get 5-year plates so it's not too much of a headache.
--Mike
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
Originally Posted by tcope
It was the Idle test that failed, by the way. I will try leaning the mixture a bit and see what happens...
Can't believe a 68 truck is being tested. Some of the states that require testing of old vehicles can opt them out if it would take a lot of money to correct it.
I might look for another shop if that option is available.
John
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
Likes: 420
From: Long Island USA
Carbon Monoxide is the result of inefficient combustion. If you passed on HC's, that probably means you are already running lean.
Without a hit-or-miss approach, the only way to get the carb right is to find an exhaust analyzer, or shop that has one, and adjust the idle mix screws until you get a low-enough CO ... Be careful, you can send the HC's way up too.
Since it's an idle test, main carb circuits do not come into play (or shouldn't, if the power valve is good). The idle screws are what you need to play with.
I've had the same problem before, and the only way to get it right was with an exhaust analyzer.
Beyond all that, if you want to try it again, do a complete tuneup (cap/rotor, wires, plugs, pcv valve, filters, etc), setup the idle screws, idle speed, point dwell, etc correctly, and see if it flies this time.
Here in Metro NY, we don't need to be tested after the car is 25 years old. Just safety.
Without a hit-or-miss approach, the only way to get the carb right is to find an exhaust analyzer, or shop that has one, and adjust the idle mix screws until you get a low-enough CO ... Be careful, you can send the HC's way up too.
Since it's an idle test, main carb circuits do not come into play (or shouldn't, if the power valve is good). The idle screws are what you need to play with.
I've had the same problem before, and the only way to get it right was with an exhaust analyzer.
Beyond all that, if you want to try it again, do a complete tuneup (cap/rotor, wires, plugs, pcv valve, filters, etc), setup the idle screws, idle speed, point dwell, etc correctly, and see if it flies this time.
Here in Metro NY, we don't need to be tested after the car is 25 years old. Just safety.
Elder User
Joined: Feb 2005
Posts: 669
Likes: 1
I can't believe you'd have to pass emissions either. If so, you might not get it. High CO can be caused by engine problems that a tuneup won't fix. What CO specification do you have to meet and what was your actual output? Usually if it's a worn engine then the CO will not even be close to passing.
Laughing Gas
Joined: Jan 2002
Posts: 1,008
Likes: 1
From: Tucson
Here's what I do every year to get my 67 352 to pass in Arizona:
* Timing at 5° BTDC (normally it's 8)
* Very lean fuel
* New PCV valve
* Add one gallon of denatured alcohol to 1/2 tank fuel ($9 per gal)
* Set the idle a couple of hundred above normal (maybe 875 or so)
I always feel as though I have gotten away with something when I pass and I usually celebrate with a cold beer. Good luck.
jor
___
* Timing at 5° BTDC (normally it's 8)
* Very lean fuel
* New PCV valve
* Add one gallon of denatured alcohol to 1/2 tank fuel ($9 per gal)
* Set the idle a couple of hundred above normal (maybe 875 or so)
I always feel as though I have gotten away with something when I pass and I usually celebrate with a cold beer. Good luck.
jor
___