Hi guys. I did a lot of searching and couldn't come up with something that wasn't fuel injected or a v8...ok so she's an 85 250 4x4 with the 1bbl Carter carbed 4.9 and a 4 speed manual. This is coming up on round 7 for smog...first one found my emissions light covered and I didn't know it. New air pump and vacuum lines to the emissions gear. Then plugs...then erg and I now have an entire new ignition system in it. Distributor to the plugs. Rebuilt the carb that was falling apart. New front cat that was a dummy from the P.O.. So here is where I sit.

15mph-Rpm-1825 co2-12.5 o2-3.3 HC max-90 meas-102 co max-.59 meas-.11 no max-753 meas-75 fail
25mph-Rpm-1609 co2-13.2 o2-2.4 HC max-74 meas-102 co max-.74 meas-.18 no max-772 meas-54

I'm so close but am almost out of ideas. I am tempted to lean out the mixture screw on the carb just for the test but, being an idle adjustment, I am doubting that will have any affect at 16-1800rpm. What am I missing here? Also, I ran a compression check tonight and all cylinders sit between 114 and 130. Manual calls for no more than 25% deviation, so were good there..

 

(let me preface this by saying I've never had to deal with CA emissions)

If I'm reading this right you're high on Hydro Carbons but way low on Carbon Monoxide and Nitrogen.
Making it leaner will not help that.
Your EGR/A.I.R. is functioning well too.

It seems it's not fuel, you're burning or passing oil.

How many miles on this engine?
Is your PCV system clean and functioning properly?
How did the plugs look when you changed them?
Does the engine use a lot of oil between changes?

Valve stem seals may be the issue.
Cheap parts, and with the old rope trick you don't even need to pull the head.
You may be able to tell just by pulling the valve cover.
They get old and brittle, then fall apart.

Otherwise it's rings and that necessitates a complete engine rebuild.
A leakdown test could tell more.

I'm sure others will have advice.
That is my best diagnosis with the available information.

 

Does Cal. have an Emissions Exempt policy? CT does not test emissions after 25 years.

 

Yes, you're reading it right..high hc, low co and no. I did some more reading last night and figured out it's not a rich or lean thing. Valve seals could very well be the culprit - a local mechanic I know was around when I was replacing the distributor and told me about the seals getting brittle and falling apart, getting into the oil pump and breaking the distributor. He was pretty confident that was the cause...makes sense i have a few noisy valves up top. I was told it had 104k on the clock when I bought it, but that could be 300 for all I know. PCV system is clean and the plugs looked healthy when I replaced them. Nice light tan but not fouled and not hot. As far as oil, it might use a quart between changes, but im pretty confident most of that comes off the bottom of the pan. Thanks for the input, looks like im pulling the valve cover tonight. Ill read up on the rope trick as im unfamiliar with it.

 

The chunks of seal won't likely get past the pickup screen, into the pump and lock up the distributor, stripping the gear.
But then your mechanic has probably seen more carnage than I ever have.

Using a piece of rope stuffed in the cylinder will hold the valve up while you take the spring off and change the seal.
It may be faster to just pull the head in order to change all 12.
Pulling the head would also allow you to check for worn guides.

The spark plugs and oil consumption don't sound bad at all.
I think you have a good engine on your hands.

 

CA smog exempt is model year 1975 and newer. They also have the strictest smog settings. On my old '81 I couldn't get it to pass for the life of me, so I adjusted timing a hair, put a new cat ($250.00) and drove it over there that day. Passed like a champ.