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Help me pass HC emissions

jms5580

Full Member
Joined
Jan 22, 2011
Messages
281
Loc.
Bozeman, MT
HC 1160 ppm (should be 300)
CO 1.03 (should be 3.00)

Timing is at around 6* advance (I backed it down, it ran great around 15*. I also backed the idle screws down a little. They are at 5 turns out now. Maybe 6 before I ran it through. I have a qjet off an 85 chevy 305, freshly rebuilt with a cold air intake. Plugs, wires, cap, and rotor were all done last year. Hardly put any miles on it since then. Couldn't get it to pass with old edelbrock but I was in the 300's at one point. I pulled the plugs quick and it seems like one is misfiring. When I pulled to gap it there seemed to be a little oil? on this specific plug. I have the plugs gapped at ~.050 or so with a pertronix flamethrower coil, opened em up a little per the instructions. Truck ran GREAT before I messed with timing and screws before the test, which I know it's supposed to run crappy with these settings. I'm also running 87 octane on a 302 with no cats, truck is a 75. Any ideas?
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,833
Close the plug gap up to about .045
Richen the fuel mix.

The low CO shows the mix is lean.
High HC shows it is probably so lean it is getting a (partial) misfire. also known as a lean misfire. The cylinder is firing, but not completly.

The 6° of timing should be fine for testing.
 
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jms5580

jms5580

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Joined
Jan 22, 2011
Messages
281
Loc.
Bozeman, MT
Thanks for the explanation! I knew I could get a lean misfire but wasn't sure how to tell or rather how the numbers were related.
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
I'd kinda suspect you may have issues with the idle curcuit on your carb 5-6 turns out is a lot more than it should be. Which I believe the farther out the screw are the richer the mixture should be. but i could be wrong on that. Some carbs are the other way around. Usually the baseline setting of about 2 turns out is very close to what they should be. you may still have a vacuum leak somewhere since the screws are that far out.

Timing at 6 degrees is usually good. but "at around" well its probably better to be at then around. you may want it at 6 degrees or below.
 

73azbronco

Contributor
Bronco Guru
Joined
Nov 11, 2007
Messages
7,796
you also may want to invest in a 2100 carb to get it past emissions
 
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jms5580

jms5580

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Jan 22, 2011
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281
Loc.
Bozeman, MT
If I almost passed with an edelbrock 1406 I should be able to pass with this. Carb was completely overhauled so I doubt it's the idle system. Possible but doubtful.
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
Either a vacuum leak or that carb is bad idle screwed back out that far point to issues. Qjunks are known to have issues. although its usally a running rich issue that they have.
 

ugly74

Bronco abuser
Joined
Apr 17, 2006
Messages
2,847
5-6 turns out is way too much. Ive run a couple of those, and they were never turned out past 2. Id suspect a vacuum leak as well
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
Make sure the base gaskit for the carb isnt leaking, the gaskit has some very thin areas that are easy for it to leak. a vacuum leak at the base gasket will cause the Quadrajet to run very rich.

hook up a vacuum guage to the motor and use that to help you adjust the mixture screws. You want the steadyist vacuum reading you can get and the highest vacuum reading you can get.

The quadrajet likes to have its throttle butterflys slightly cracked open at idle so back out your idle position screw untill the throttle is fully closed and screw it back intill it slightly lifts the throttle this will ensure that the throttle is cracked open enough.
now start the engine and set the idle screw to keep the engine running at 1000 rpm. now adjust the idle mixture screws to get the highest steady idle.
if the rpms goes higher than 1000 rpm lower the Idle screw back down to 1000 rpm. once you get the highest steady vacuum reading at 1000 then lower the idle down to 800 rpm using the idle mixture screws not the idle screws
at that point your done if you have a manual transmission. if you have an automatic transmission put your brakes on and hold it in gear you will have to adjust the idle screw to give you 800 rpm when your stopped in gear with the brakes on.

in order to pass emissions at idle the vacuum reading must be very steady and at its highest reading you can get at idle. any miss fire or vacuum leaks or engine problems will show on the vacuum guage and will need to be fixed.
passing emissions if far easier at idle speeds in the 800 to 1000 rpm range the engine must be at full normal temperature it helps to run a 180 degree thermostat or higher. Also run Chevron gas at the lowest octane that runs properly in your engine. I would run a tank of this gas through the engine before you go to testing it will help clean up what ever hasn't been properly burning. Make sure you tune the engine to the gas your going to use in the test. dont tune it to Arco gas and then run Chevron or tune to Chevron and switch to some other brand. After the test run what ever you want.
most emissions tests will fail you if your timing is incorrect which for you is 6 degrees before top dead center at idle with the vacuum hose to the vacuum canister disconnected and the hose plugged for the test.
Idle speed range is more open but most will fail you if your too high and thats usually above the 1000 rpm range.
I guess its set at or its about there isnt going to cut if especially if your set-up is hard to tune. get the tools or borrow them and get things set right and you should sail right through these tests as the lee way is so large on these older trucks.
You need a tachometer, a vacuum guage, and a timing light and alot of patience.
 
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jms5580

jms5580

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Jan 22, 2011
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Bozeman, MT
I don't suspect vacuum leak because it dies before I can get the one screw all the way in. I pulled the plugs to re-gap at .045 and they were very white/ashy so I'm assuming it was lean. I put premium in it...which sounds like it was a bad idea the more I think about it so I'll have to do some driving. I'm also running a cold air intake, which I know isn't much but it's going to affect the density of the air coming into the carb right? Therefore richer mixture needed? I'll keep playing. Thanks for the suggestions.
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
Well your not suspecting a vacuum leak is your issue. deny it all you want but i'm pretty sure you have one. white plugs say it all means its lean might ot even want to drive it until fixed as running to lean can damage the engine.
Check the torque on your intake manifold. Some vaccum leaks are virtually undetectable. Your cold air intake is not doing anything.wouldnt worry about it.
 
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jms5580

jms5580

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Joined
Jan 22, 2011
Messages
281
Loc.
Bozeman, MT
I ran propane all around the carb. Tried starting fluid as well. That's why I assumed there was no vacuum leak. I will check the intake manifold next.
 
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