Sounds like your car is getting into excellent shape. The emissions just needs some carburetor adjustment.
Quote:
wanted to reduce fuel mixture so changed the carburetor jet from 75 to 65 size
When emission technician suggest mixture changes, they usually mean the idle mixture screw.
Larger jet will increase HC. However I think he changed the air bleed. Stock size is about 60.
Changing these does not affect the idle circuit. I see from the results that you idle HC and cruise (2500 rpm) HC both increased.
Suggestions:
1. Replace the larger air bleed with the original one. A too lean air bleed may case misfire, raising both HC and CO
2. Set the idle speed to 800 RPM -- 1100 is RPM is to high for the idle circuit to work properly
3. Adjust the idle mixture per Datsun instructions
Tune-upAdjust carburetor at full operating temperature. Verify choke is fully open before adjusting
manual: 750 best idle, then lean to 700 rpm
automatic: 800 best idle, then lean to 770 rpm (check for 650 rpm in drive after adjustment)
"best idle" means the smoothest idle (first speed screw, then mixture screw, repeat until found)
"lean" means turn the screw in until the speed drops (mixture screw only)
For minimum emissions and fuel economy the idle mixture should be slightly lean. Petrol engine runs fine from 14:1 (slightly lean) to 12:1 (rich). But at about 14.7:1 achieves minimum emission combination.
Transfer
