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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53901
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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I have a Mercedes 1976 280C and it does not pass smog test.

Customer Question

I have a Mercedes 1976 280C and it does not pass smog test. CO is 11% Hydrocarbons are three time allowed level. It looks like fuel mixture too rich. Car has lots of power. Replaced spark plugs and points engine running fine my next step wiil be to lean the carburetor by turning fuel mix screws in. On the carburetor it says SOLEX A1. The problem is I cannot find the fuel mixture screws I can see a screw on the bottom front left of the carburetor. I think that is one There is suppose to be another on on the left but there are connections there instead. Where are the fuel mixture adjust screws? Or does it only have one it seems to be a double barrel carburettor.
JA: What specifically didn't pass the test? When was your last oil change?
Customer: I mean another on the right when standing in front of the car
JA: What is the model of your '76 Mercedes?
Customer: 280C I do not drive it much oil change 2 years ago .
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: I have only replaced the spark plugs and the points and reset the idle. I have put in a new air filter.
JA: Anything else you want the mechanic to know before I connect you?
Customer: That is all i can think of
Submitted: 9 months ago.
Category: Mercedes
Customer: replied 9 months ago.
HC Max 201, measured 493, CO Max 1.3, measured 11.00 NOX max 1314 measured 150 clearly too much fuel too little air. at 15 mph
Expert:  Marty replied 9 months ago.

Hi, my name is***** mixture screws are located at the base of the carburetor right next to the two electric solenoids. It's definitely running too rich at idle. Check the secondary throttle plates and see if they are closing at idle. If they remain open it will draw additional fuel in through the secondary barrel. If you cannot lower the mixture you will probably need to rebuild the carburetor.

Let me know if you need further assistance.