Didn't pass emissions. Help?

thecantaloupeman · Jun 21, 2020

So I have been driving my truck with the carb quite rich for a while. I didn't think it would affect my emissions test that badly, but the CO2 was at 5.79 and it is supposed to be under 5.50. I went home and adjusted it, but I am pretty trash at adjusting the carb.

I started by screwing all the way in and turning out 1.5 turns, then starting the engine and backing the screw out until the RPM stopped going up. At a certain point the RPM stops rising and the vacuum doesn't rise or drop. Is that where I want it to be adjusted? Isn't the vacuum/rpm supposed to start dropping again and then you turn it in the opposite direction?

Is all the way in lean and all the way out rich? Is it safer to be lean on the emissions test than rich?

C10MixMaster · Jun 21, 2020

was th

thecantaloupeman said:
So I have been driving my truck with the carb quite rich for a while. I didn't think it would affect my emissions test that badly, but the CO2 was at 5.79 and it is supposed to be under 5.50. I went home and adjusted it, but I am pretty trash at adjusting the carb.

I started by screwing all the way in and turning out 1.5 turns, then starting the engine and backing the screw out until the RPM stopped going up. At a certain point the RPM stops rising and the vacuum doesn't rise or drop. Is that where I want it to be adjusted? Isn't the vacuum/rpm supposed to start dropping again and then you turn it in the opposite direction?

Is all the way in lean and all the way out rich? Is it safer to be lean on the emissions test than rich?

was that co or co2 and what were all the numbers?

MisterB · Jun 21, 2020

I'd put in a good strong gas additive and drive around for a bit to get things cleaned out and then connect a vacuum gauge to dial in the carb

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DoubleDingo · Jun 21, 2020

And drive it around for about an hour before going in. You want it good and hot, not just fire it up and go in. You having the C20 you can pass a whole lot easier than the C10 guys.

The way I was taught to adjust a carb, turn the screw in until the engine stumbles, back it out until the engine smooths out, then another two turns out. Repeat with the other side. And repeat again with both a time or two to get it idling like a sewing machine. And make sure the timing is set properly, and the ignition components in good working order. As mentioned, a quality fuel system cleaner will help too. After you do all of that, make sure to drive it an hour before going in. I said it twice because it is important. And leave running while you wait for the test, that'll keep things good hot.

nabeshin · Jun 21, 2020

Set up an LLC in Montana and forget about taxes, registration, and emissions testing forever.

thecantaloupeman · Jun 21, 2020

DoubleDingo said:
And drive it around for about an hour before going in. You want it good and hot, not just fire it up and go in. You having the C20 you can pass a whole lot easier than the C10 guys.

The way I was taught to adjust a carb, turn the screw in until the engine stumbles, back it out until the engine smooths out, then another two turns out. Repeat with the other side. And repeat again with both a time or two to get it idling like a sewing machine. And make sure the timing is set properly, and the ignition components in good working order. As mentioned, a quality fuel system cleaner will help too. After you do all of that, make sure to drive it an hour before going in. I said it twice because it is important. And leave running while you wait for the test, that'll keep things good hot.

I might try the fuel cleaner. What kind would you recommend? I probably have the carb adjusted better than it was before. Because I did almost exactly what you described yesterday. It still smells a bit rich but that fuel cleaner could definitely help.

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C10MixMaster · Jun 21, 2020

I would do the lean drop on the idle mixture screws, back it out til it smooth and back it out an additional 1/2 or 1 turn.

thecantaloupeman · Jun 22, 2020

C10MixMaster said:
I would do the lean drop on the idle mixture screws, back it out til it smooth and back it out an additional 1/2 or 1 turn.

So does backing out the screws make it more lean? Or does that richen the mixture?

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C10MixMaster · Jun 22, 2020

thecantaloupeman said:
So does backing out the screws make it more lean? Or does that richen the mixture?

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in lean, out rich

HotRodPC · Jun 22, 2020

Probably a half turn in on each and you'd have passed. That's some ****** **** right there. You'd think the testing tech could have been a pal and did that while it was on the sniffer since it was so damn close. You're HC's is wayyyyyyyy in the green. That's likely to go up just a bit though as the CO comes down but you're still going to be just fine.

Does Coloarado use state ran testing stations or do they use state licensed shops to do inspections?

Craig 85 · Jun 22, 2020

Check your timing and idle speed also.

Bextreme04 · Jun 22, 2020

The instructions for setting my 74 C20 with a 350 4-bbl were to start at 1-1/2 turns out. With the engine in "D" with the parking brake set and the wheels chocked, adjust one idle screw slowly 1/2 turn at a time until the rpm maxes out(adjusting the idle as you go to keep it around 700rpm. Once you get it to peak, and it is at 750rpm, screw IN the screw 1/4 turn at a time until the idle drops to 650rpm. Repeat on the other idle screw. This worked wonders on my 74 C20. It will set it to be slightly lean at idle, which is what you want for emissions, fuel mileage at cruise, and cat longevity(if you have one).

SquareRoot · Jun 22, 2020

LS Swap and take it back.

thecantaloupeman · Jun 22, 2020

Bextreme04 said:
The instructions for setting my 74 C20 with a 350 4-bbl were to start at 1-1/2 turns out. With the engine in "D" with the parking brake set and the wheels chocked, adjust one idle screw slowly 1/2 turn at a time until the rpm maxes out(adjusting the idle as you go to keep it around 700rpm. Once you get it to peak, and it is at 750rpm, screw IN the screw 1/4 turn at a time until the idle drops to 650rpm. Repeat on the other idle screw. This worked wonders on my 74 C20. It will set it to be slightly lean at idle, which is what you want for emissions, fuel mileage at cruise, and cat longevity(if you have one).

How am I able to tell the RPMs without a tach? Is there a tool I can buy?

I passed emissions with all of your guys' help, but I still need to adjust my carb correctly now. I leaned it out as much as possible with the engine still running smooth. I got home and tried adjusting to max vacuum with the gauge and now it smells really rich. Maybe it is because I have a lot of vacuum leaks, so I might try adjusting it like how you said.

thecantaloupeman · Jun 22, 2020

SquareRoot said:
LS Swap and take it back.

LMAO I'd love to

Didn't pass emissions. Help?

thecantaloupeman

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C10MixMaster

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DoubleDingo

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nabeshin

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thecantaloupeman

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