As a follow-up to our guaranteed time program AGBSTARS, we propose SWS Fabry-Perot observations of Q-branch lines of HCN and C2H2 at around 14 micron in four carbon stars and one S-type star. The goals of this proposal are: (1) To detect HCN lines which are only just visible in our guaranteed time observation with SWS01. (2) To determine the abundance, excitation temperature, and turbulent velocity of C2H2 and HCN from the observed data using detailed model calculations. The comparison of the results for the two molecules will indicate the origin of the lines and the physical structure of the circum- stellar shell. (3) The results will also be compared among the target stars as a function of mass-loss rates and C/O ratios, to find the relation between the excitation status of the molecules and other properties of the stars. It is well know that HCN and C2H2 are two of the most abundant molecules after CO in the atmosphere and the circumstellar shell of carbon stars. C2H2 is one of the major source molecules for the carbon chemistry in the circumstellar envelope. HCN is a key molecule concerning chemical processes nitrogen involved. To understand the behavior of the two molecules in the photospheres and the circumstellar shells of different types of star will contribute to our knowledge of circumstellar chemistry. It is especially important for C2H2, since this molecule cannot be observed by radio techniques. On the other hand, the richness of the molecules in carbon stars means these molecules could be a good probe for investigating physical structure of the circumstellar envelope, such as temperature or turbulent velocity. The narrow line separation in the Q-branch enables us to obtain information of several lines together in a small scanning range. This makes the interpretation of the data easier and increases the confidence of the results. ISO is the only available instrument which can observe at 14 micron (outside the atmospheric window) with a resolution of about 30000.