Too high Hydrocarbon on emission tests-Help

[justhorns]

My great chevy C-10 "ralph" with a 250-6 has just flunked Colorado emissions 8 times. Too High on hydrocarbons (although I have gotten very close to the spec. The Spec is 220 PPM and I have gotten it to 226 on the 6th of 8 tests. They still flunked me after being up at 900! Stinkers.

The engine purrs like a kitten. Spark plugs look good. Truckl runs great. Carb (a Varajet II) has been rebuilt.

I've adjusted mixture with the mixture screw, I've adjusted timing, I've installed all emission equipment that is still functioning. I'm trying not to spend on expensive fixes at this time. Truck is no longer registered due to this issue (expired 7/31/25).

Anyone have ideas?
One option is carb replacement, but, adapter plates are available from the netherlands for a weber, then buy a weber (32/36 dgv), then kludge up a linkage.. air cleaner. I know this varijet II on this truck is a POS, but, its easiest to just tweak what needs tweaking, and cheapest too.

 

[Grit dog]

She got a cat?

 

[fast 99]

With functioning cat and air pump results are usually lower. What is the CO? Also where is the RPM at? If RPM can be raised that will usually lower both HC and CO.

Didn't see the test sheet, too lean at idle. That will cause a misfire resulting to high HC.

No RPM reading, 1350 limit [boy that's a high limit] gives you lots of room for adjustment.

 

[Ricko1966]

Retard the timing a few degrees. That will lower the reading. You are so close now I'd assume that's all you need to do.

 

[justhorns]

It has a catalytic converter under there. I think its the original. It does not have an air pump, but uses pulse valves to draw air in from the crankcase. I will try didling with timing, its easy to do. Then I'll run it through again. I'm afraid of replacing the cat as it doesn't get enough air in through the air pulse horsehockeysticks so a new cat might not be happy.

 

[fast 99]

Am surprised is runs smooth when it's that lean. The cat and pulse systems may be working fine with those test results. Retarding the timing is a good idea and worth a try however I suspect the engine would be happier with more fuel.

Although not approved by Washington state EPA checking the inlet and temperatures can give you an idea if it cat is working. There should be at least a 50 degree increase post cat.

 

[justhorns]

I have been richening it up, and it seems I went too far. The adjustment screw is really hard to get at, and I had to make a special tool to get at it. When the engine is warm, I can't get anywhere near it as it sits near the exhaust manifold. Based on results of tests 7 &8,I have taken fuel out of it.

 

[goldpack]

I live in NY State and when they were probing exhaust they only did it in the more urban counties where the air was really smoggy
... but the residents of such counties were not obligated to get a inspection in them....so one could just drive out to the sticks and pass. its always been local garages though,

I live in the sticks and its just ODBC2 plug in,
and with a 25 year old antique (based on listed model year) just a plain old safety inspection. not that many antiques can survive the rust anyway, so anything stinky with hydrocarbons like a 1970 so what.

but I digress, @justhorns can you get out of stinky/busy clusterfruck Denver and pass without a similar test ?
Sell to someone have it in Wyoming etc ? You or someone else Repower it with a engine out a a wrecked 90s truck ? (Preferably with the whole thing next to your truck so you can pick cheap at it for all the goodies stem to stern)

 

[fast 99]

I have been richening it up, and it seems I went too far. The adjustment screw is really hard to get at, and I had to make a special tool to get at it. When the engine is warm, I can't get anywhere near it as it sits near the exhaust manifold. Based on results of tests 7 &8,I have taken fuel out of it.

Perform a lean drop for idle mix. Either by ear or a tach back screw out until highest rpm is achieved then back in until you loose 25-50 rpm.

 

[DoubleDingo]

Good recommendations on the adjustments needed to pass.

How long are you running it before testing it? If not driving around for at least 40 minutes, you need to.

You're so close, with the adjustments recommended you should get it, but if it's original cat, replace it too.

 

[Hilllbilly]

I had to replace my charcoal canister once . IIRC it was full of gasoline

You got a charcoal canister smog crap with the fuel fume lines?

 

[Sad Sack]

Pour in some catalytic converter cleaner in the gas tank like Rislone Cat Complete or CataClean, got nothing to lose other than about $20.

 

[dd1990]

I have been richening it up, and it seems I went too far. The adjustment screw is really hard to get at, and I had to make a special tool to get at it. When the engine is warm, I can't get anywhere near it as it sits near the exhaust manifold. Based on results of tests 7 &8,I have taken fuel out of it.

If you have the original pancake cat that may be your problem, those cats are junk the beads have to replaced. A new cat with a the honeycomb design flows more and burns off excess fuel emission way better. You don't need air or air injection to run a cat, my suburban has a cat but no air or pulse air injection.

 

[bookit]

How much oil does it use, even a little oil consumption can distort your emissions output, also check for any exhaust leaks. and repair them.

 

[justhorns]

OK, thanks to all. I set the timing to factory stock settings, and it came in immediately. I have passed emissions and am re-registered for another 5 years! See photo below. Big changes with little effort.