Volkswagen: 1979 convertible beetle (karman edition), flat head screwdriver, exhaust gas analyzer

Question
Our recently purchased beetle runs great but recently failed emiisions for hydrocarbons (535 at rpm 400 is pass)what are the most likely causes?   (chilton)

Answer
Hi Don,

Most likely it is the CO adjustment screw (mixture) on the intake air sensor.

It is located upside down to the left if you are looking at the air-sensor dead on.

This screw will need to be adjusted with a flat-head screwdriver and the use of an exhaust gas analyzer to ensure it is within spec.

Good Luck!

Ron