car passed mot yesterday( Pinto 2.0)on carbs.Noticed co level was 2.5% (4.5% allowed) and 275ppm HC (1200 allowed) can anyone tell me if my engine is running weak/rich and explain the relationship between co/hc

co level reflects how rich you engine is running and the HC level reflects how healthily it is running.

Pinto engines will run healthily with the CO level between 0.5% and 4.5% (the lower the figure, the weaker it is running and the higher it is, the richer it is running) but the ideal level for a car engine is usually about 2.5%.

HC or Hydro-Carbon level is a measure of what unburnt fuels or oils there are in the exhaust, thus telling you how healthily your engine is burning the incoming fuel mixture. A high reading can reflect an airleak or excessive oil consumption and this needs to be assessed in conjunction with the CO level but a again a pinto engine running on carb(s) I would expect the co level to be somewhere around the 300ppm mark (+/- 100ppm depending on age of engine and carbs).

SO your figures are just about perfect for a carb engined vehicle that is not brand new but has probably got some where between 10 and 50k miles on the clock.

hope this helps.

[Edited on 4/6/10 by jollygreengiant]

excellent reply,thanks

steve