Okay well how old are the spark plugs in general? If those plugs have been dropped in the past or just old they would not work the same and could misfire etc.. How about the distributor cap does it have small cracks in it look underneath and check each point aswell are they worn down? Spark leads are not likely the culprit but that could be another cause get a multimeter and check their resistance.

If they are the two lower compression cylinders then do a valve adjustment first if not improvement it's more than likely the rings are shot. Fill those cylinders with some oil and redo a compression test if you have an improved reading you know the problem.

Tom,

Thank you will try that.

Thanks a lot.

Gavin,

I have new distributer cap,rotator,plugs etc..Will get the valve adjustment first and see what happens.By the my 71 Z is the same color of yours.

Thanks a lot.

Oh btw do you know if your running a points distributor or an electronic distributor?

It is a point distributor.

Thanks

I finally solved #3 and 4 cylinder spark plug fouling problem !!!!.

By using a gasoline additive that cleans the engine and the valves the problem is solved.

If you have a car that has not been used for a long time,2-5 years like mine,you might have the same problem..

Thanks to everyone that advised me what to do....