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high HC values!!

1716 Views 4 Replies 3 Participants Last post by  Ennio
Hello guys, I had an emission test on my 82 gtv2.0 (alfetta-gtv) equipped with, twin Dellorto DHLA 40mm, sport cams (don´t know specs since they came with the car), Ram flo sport filters (400 cfm), Mallory 6AL ignition box (same as MSd but digital), accel wires and superstock coil, new cap and rotor. Here are the readings I got:

at idle (1000rpm):
CO: 5.27%
CO2: 9.48%
02: 3.65%
HC: 2346ppm
Lambda: 0.947

at 3000rpm:
CO: 0.66%
CO2: 13.92%
02: 1.36%
HC: 515 ppm

I need your help regarding this issue. The HC levels are way TOO high and I think this is due to the carbs that are giving too much fuel. The guy told me that the idle jets are uncorrectly set, but I don´t think so.The car doesn´t have a rough idle, but maybe the mixture is too rich at idle and I´ll have to lean the mixture with the idle mixture screws. Am I correct? please I need help here. I don´t have a synchorometer and never have done this job. Is it easy with that tool? or is there another way? I am a newbie Alfa, since I am going to have the car 1 year soon.

Thanks in advance.

ps. The car doesn´t have anti smog equipment since it is an Euro version.
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The 5.27% CO at idle is indicative of an overly rich mixture. You should be able to get it down to 4%, or maybe a little less, and still have a smooth idle. Here is a good thread on Weber carb syncronization -
I`ve used a synchrometer and a colortune to balance the carbs and to adjust the mixture of each cylinder. Now tha car feels smoother, runs great and it will hold a very low idle. I have to re-test the smog to see the new values at idle and at higher rpms.
Thanks for the advice.

Unfortunately I found that of 3 of 4 plugs were sooty, due to the rich mixture, and one (cylinder 3) has some oil residues (oil was present also by the surroundings of the sparkplug). I am worried about this finding, the car had the rings and bearings changed by the previous owner (a engine refresh) but no work was done to the cylinder head, so I suspect of worn valve guides..
High HC generally means poor/incomplete combustion, and usually is a misfire condition. Are the idle circuits in the ballpark? The very rich condition could be wetting the plugs to the point where you're getting misfire, so you'll have high CO (richness) and high HC (misfire).

These kinds of carbs have a hell of a time meeting smog standards.

Thanks for the advice Andrew. I´ve just balanced the carbs using a synchrometer and adjust the micture using a colortune, and took it to have an exhaust fumes test. The CO was about 1.96% and the HC 1600, we took some gas out of each carb and got the CO to 3% and the HC to 600. I then figured out with my mechanic that the needle valves of the carbs were worn, and that the fuel pressure was about 7psi. I installed the fuel regulator (factory) and we got it down to 3.5 which is to low for the webers, I took it out and I am running the car as is.

I´ve just ordered the new needle valves, I will change the fuel pump, install the filter/regulator, re-adjust the carbs and see waht happens.

You are right, when I adjusted the carbs, cylinder´s 3 plug was wet, I checked the plugs today after using it a while with the new adjustment, and it was completely dry.
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