1968 Coupe 289 with Hollybrock performer carb and manifold. I'm totally baffled as to why the engine is missing when ticking over on the last two cylinders on the left side at the back. When i take off ht lead of either of the last two cylinders it makes no difference, although there is a good spark shooting across to the plug, when you rev up it seems to clear. My last resort is to remove the heads thinking that it could be burnt vale or sticking valves, compression on the cylinders are between 130-140. I have checked the timing, points, distributor cap, coil, all the obvious things, with no success. I would be glad of any ideas.