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Posted by D Sherman [72.47.9.228] on Wednesday, June 16, 2010 at 23:54:43 :
In Reply to: OT-flathead woes Ford 8N posted by J. Veitti [69.144.190.102] on Wednesday, June 16, 2010 at 22:19:53 :
My thinking is if it's clearly only one or two cylinders that's bad, then the problem isn't going to be anything that's common to all the cylinders (carb, coil, fuel, etc). The only thing that's unique to each cylinder is compression and spark. The compression is good on all of them, so that leaves spark. You shotgunned it pretty well, so you would think all the new stuff is good, but maybe a plug wire isn't really seated in the cap or on the plug? Maybe a wire got broken internally? How does the cap look inside? You can check the resistance of all the plug wires. If they're suppression (carbon) wires, they'll be in the range of a few thousand ohms each, depending on length. Anything over 10,000 ohms or so is getting doubtful. Cracked plug maybe? Just for kicks, swap a wire and a plug, together, from one of the known good cylinders to one of the known bad ones and see if the problem goes with the cylinder or with the wire/plug. A timing light, clipped over each plug wire in turn, will tell you if the plug is firing. The timing light pick-up responds to current flowing through the plug wire, so if no spark, then no current, and no flash of the timing light. Another thing you might do just for kicks is get it running, and briefly bypass your ballast resistor. You can do that for quite a while without burning out the coil. If the engine smooths out, it's at least a hint that you have a weak spark condition, which isn't necessarily due to a weak coil.
Another way of thinking is that if the plugs are fouling, the mix must be igniting, but for some reason it's much too rich on those two cylinders. Obstruction in the manifold? Vacuum leak at the front of the manifold forcing you to run with too much choke, which in turn keeps the rear too rich?
There used to be a guy on this forum who went by the name of Willy-N. I think his real name was Mark Hendershot, or something close. He dealt in 8Ns a lot, buying and selling them. Maybe you can track him down from the archives and ask him.