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MG MGB Technical - Almost passed Emission test.... need help

Well, as the title suggests I came very close to passing the Georgia emission test this week in my 79B but I was a little too high on CO in one part of the multi part test that is required here in Atlanta.

Here's what I have: 79B w/ 72 model exhaust system, no catalyst, stock dizzy with advance routed directly to a Weber 36/32 DGV carb.

Here's what I got on the test:
25 lb load at 25mph:
Reading allowable
HC ppm 245 495 Pass
CO % 3.27 3.56 Pass
NO ppm 1301 3181 Pass
CO+CO2 % 8.5 6.0 min Pass

50 lb load at 15mph:
Reading allowable
HC ppm 233 503 Pass
CO % 3.61 2.58 FAIL
NO ppm 1055 3416 Pass
CO+CO2 % 8.7 6.0 min Pass

I would like to be able to tune this problem out but I am not really sure how. I did not do any tuning before the test except set the idle and fill up with EXXON 87 octane so it may be dirty plugs or oil if it is feel free to tell me to go away and quit bothering everyone.
Thanks in advance for your help.

Eric
Eric

Do you still have the air pump? If so, is
it working?

On my 79 (with cat and Zenith carb) mixture is
set to 5.5% with the pump _disconnected_.
When I reconnect the pump, CO falls way down (below
1%) A working air pump will have a big effect on CO.

If the air pump is connected and working, it sounds
like the carb is too rich.

The HCs are somewhat high (although well within
passing.) Again, if the carb is too rich, HCs
will be high (or if there is an ignition or valve
problem.) But without the cat converter, HCs may
be pretty high anyway.

I don't think the cat affects CO much -- any comments?
Ronald

Ronald. I agree with your analysis. I am not familiar with the type of testing that Erik describes. Our testing is at idle and at a "cruise" as dictated by a computer. Normally, the test operator has the MGs in third gear when testing the "cruise" function. HC can go up either due to a too rich mixture or due to a too lean mixture (causing a "lean miss"). CO tends to go down as the mixture is leaned, being lowest at the chemically correct or Stoichiometric mixture. (According to the manual with the gunson's CO meter.) I would consider having the car professionally tuned for emissions. It may be necessary to add an aftermarket, free flow cat to make the car pass Erik's testing requirements. But, as a first step, I would see if leaning out the idle mixture a little, to an acceptable CO reading, would solve the problem. Les
Les Bengtson

Eric,
Also, before taking the test, drive the car at least 15-20 miles to fully warm it up, and try not to shut it off before testing. Since you only failed on the one point, it's possible that something as simple as a dirty air cleaner could be messing you up; change or clean that for sure. By all means, have a good mechanic tune it for emissions testing. My '68 GT passed the second time in WA. state after an import specialist mechanic tweaked it, and the air pump had already been removed by the PO. Good luck, Joe

Joe Ullman

This thread was discussed on 19/09/2002

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