I have a 81 B-150, It starts and runs great. It uses no oil, and the compression is good. It has about 95K miles, all original equipment including the lean burn system controlling the carburetor and ignition systems. I constantly have problems passing the emission part of the yearly state inspection because of high levels of CO. Any ideas to help lower the CO levels would be appreciated. Thanks !

If your truck has smog equipment on the engine, there's probably a trick you can do to have it running full time. In my Land Cruiser all I have to do is connect a constant vacuum to the VSV that controls the air induction system. After I'm done testing I just put it back.

A couple other things to make sure of:
1) Make sure your catalytic converter is still in good working order (if you have one)
2) Don't sit at idle while waiting in line to be tested, and keep the wait as short as possible. Idling only lets crap build up in your system, so the butt sniffer picks it all up.

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

Are you failing CO% at high rpm's (2500), idle rpm's, or both? High levels of CO indicate elevated quantities of unburnt/incompletely burnt fuel, so it sounds like you are running a little rich. So if it is only failing at idle then leaning out the idle mixture screw 1/4-1/2 turn should cure your problem. If it's failing at high rpms or both, then the jet may be too big...but if it runs good id leave it.

One "quick fix" is to get down to a 1/4 tank of gas and dump in 3-5 bottle of iso-heet or other fuel system drier. This usually leans out your mixture enough to get past the sniffer. After the test, fuel up and youre good to go for another year.

-Aaron

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The "Silver Bullet"
87 Ram D150

Good ideas, I did have the catalytic converter checked for excessive back pressure and it seemed ok, but that doesn't mean it is working effectively, it is 22 years old. The CO's are high on both idle and high speed. They do the test on a dynometer so the technician runs the vehicle at two different speeds. With this lean burn system, It appears to me, that the mixture adjustment screw has been factory set and is not available to manual ajustment. I think it is running rich, as you suggested. You can smell unburnt gas and you can see black smoke. especially on start up. I like the idea of changing the jet size because it is something that I can actually do. thank you, Guest

I'd replace the needle/seat and float, first. If that doesn't do it it, I'd try dropping the float level a 1/16" at a time. I wouldn't go over 1/8" below stock, though.

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'70 Cuda AAR
'74 Duster 360
'79 MagnumGT
'79 Chrysler 300

I don't think that your carburetor needs rejetting ,not if it has the original size jet in it. A major reason catlytic converters clog on these trucks is that
the holley 1945 carburetor malfunctions.Mine would run rich from internal leaking and also had a lean missing problem on acceleration. A factory rebuilt holley 1945 with tight throttle bushings might be a better solution to your problem. Also if you egr valvr is more then a few years old I would replace it. Get a can of WD-40 and spray around the intake manifold, carburetor, egr valve and vacuum hoses while the engine is running and listen for a change in rpm. A change in rpm indicates a vacuum leak. Another thing to check is your coil voltage while the engine is running. I don't think your truck came with a balast resistor so your coil voltage should be within 1 volt of battery voltage while running. I had a cheap rebuilt alternator on my truck and it would start to idle rough and missfire at a traffic light with the AC and lights on. It was only getting 10 volt to the coil. Things like this will cause you to fail the emmissions test.
Good luck!
D150

My 87 originally had a lean-burn ignition, i never had more than 8.5 volts at the coil--the computer controls the voltage instead of a ballast resistor.

The stock 1 bbl holley (feedback type, whatever the POS was) on it was adjustable, but there was a cap over the adjustment screw that i had to break off to get at it. My truck never did run quite "right" with that lean-burn and holley 1 bbl....i can relate to your pain.

Id only re-jet you carb as a last resort as well. Some other things to check:
Is EVERY vacuum line/hose in good shape/not leaking AT ALL? Even one tiny vacuum leak wreaks havoc on the way lean-burn ignitions work(or dont work) Real quick way to check how the lean-burn is working...check your timing. If it "wanders" at all at idle, youve got a vacuum leak somewhere.
Carb bolted down tight?
What do the spark plugs look like? Gapped properly?

Just some ideas, id personally find a way to get at that idle mixture screw.

-Aaron

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The "Silver Bullet"
87 Ram D150

I put my 1971 Valiant on an emissions machine once last fall just to see what it would read. One of the readings, I think it was the hydrocarbons, was over 3,000 at idle. I played around with my idle mix screws and got it down, but put them back up because my moderately built /6 likes a rich mixture to idle well.

The car is emissions exempt and never had a catalytic converter, but I'd run it emissions illegal anyway. When I cold start it, I don't smell any gas (ever), but the exhaust will turn the snow on the ground behind the exhaust pipe black in only a minute or 2. So what? As long as it idles good, that's all I care about.

Thanks for all your inputs. This is a great web site. I'll concentrate on the carburetor first, as suggested. Back in aug. 98 with about 79K miles (now @ 95K), I removed the carb and had it rebuilt. And that certainly helped the CO levels then. It doesn't seem like after only 16000 miles that it should be rebuilt again, but this van sits around alot, gets driven to go fishing, very few short trips. So, time sitting might be a bigger factor in messing up the carb than miles running. I changed the sparks last at 76K miles in sept 97 so they probably do need replacing as suggested, as well. A local mechanic who likes older Dodges, suggested that I replace the Electronic spark control system with an ordinary Electronic Ignition. This involves a new ECU, ballast resister and distributor. It seems to me that the carb would also have to be replaced but I don't know. Another local mechanic from a nearby Dodge dealership suggested that I just leave that part alone. I'm leaning toward leaving it alone and just concentrating on the carburetor. Thanks again, Quest

Whatever you do, do one change at a time, so you know what did what. Keep us posted as to what you find out, so we can all be a little wiser.

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'66 Cuda 225/4spd
'66 Dart GT convertible 225/auto
'64 Dart GT 340/4spd

My 1987 D150 has no emission control equipment whatsoever. the first time I had to pass emission testing after my extensive modifications, I went to my local farmers co-op and bought about three gallons of methal alcohol, ran my tank nearly dry and dumped it in. I passed with half the allowable limits! The truck ran like crap on the way there and would only go 45mph but as soon as I left I went straight to the gas station.