I have a european 308 1979 carb model, which is only firing on 6 cylinders. The car has been checked for compression, plugs balance and mixures that are all Ok and I have been told it is probably tight valves. From this I have been told to take the head off, check the clearances and reseat the values. Is it worth trying a valve clearing fluid in the fuel or is this likely to cause damage to the valves and engine? The valves on the car I believe are sodium. Thanks for your help.
You question/explanation seems a little strange. Having a "good" result from a compression test is not consistent with a valve (or two) not seating properly. Also, it would be impossible to confirm the mixture is "OK" on a cylinder (or two) that isn't actually running. Can you explain further? I.e., by "not firing", do you mean that two cylinders aren't contributing any useful work, or that you have no ignition spark on two cylinders?
I have been told the igintion system is operating fine. The valves it appears are not opening properly to allow the fuel into the cylinder therefore not firing and the car backfires on acceleration. Any further thoughts.
It is virtually IMPOSSIBLE for an engine that has good compression to have tight valves that would keep a cylinder from firing. Find a different mechanic ASAP, before you end up like Mr. burned valve 348, or Mr. siezed exhaust cam. Both these fine gentlemen seen incompetent mechanics who who called themselves Ferrari Techs, who have nowcost them $$$$$$$$ in extra unnecessary repairs to correct the problems.
Ask for the numbers, both for the compression tests and valves clearances. Post them here ... How do you know (or have been told) that two cylinders are not firing?
With all due respect to the posters above it is possible that the cam lobes have become rounded, fractured tappet bucket or missing/damaged adjusting shims. Many years ago I saw a 206 SP which rounded it cam lobes due to inadequate lubrication. I suggest you pull the valve covers and take a close look at the valves/cam lobes on the affected cylinders.
