Hello, All I’m going to try to keep this short, but include the details that might help diagnose my current running issues. I’ve got a 59ab engine that I picked up two years ago. It was unknown condition except that it ran and didn’t smoke. Tore into it a little and it was super clean. Compression test showed 100-110 in all cylinders except #7 which was 90. It looked to have been rebuilt with std pistons, adjustable lifters, and oem valves. Ran it with dual 97s on an Offenhauser intake, and a Stromberg Efire distributor all last year without issue. Ok, so, of course I couldn’t leave well enough alone and this year put on a Edelbrock slingshot intake, vintage rebuilt chrome 97s, and Ford factory aluminum heads. Judging from the smell it was running pig rich, but I drove it around for a couple weeks like that anyway, because I was too excited. One night I’m coming from work (about a ten mile drive each way) and she just starts chugging. Sounded like she was missing badly and loosing power until I could barely get her going after stopping. Pulled the plugs and they were all black as sin. Well, I figure it’s time to re-jet now! I also changed the coil out for my spare just in case. I know you shouldn’t change so many things when diagnosing a problem, but I really wanted to get back on the road. I end up jetting down from .43 to .39 and going from a #69 pv to #71. I also make sure to use new gaskets for everything I tore apart and set the floats. She fires up, plugs are golden, I’m motor-vating once again. WELL, a couple nights ago it rains heavily while I’m parked outside. I have an open engine bay, but I covered the carbs beforehand, so no harm (that I could see). Rain stops before I leave, but on the way home she suddenly starts sputtering again. I limp home, and when I pull the plugs they’re black again! #4 is exceptionally oily. I’m thinking the rain must have gotten something wet that didn’t want to be wet. In any case, I test the resistance of my suppression core 8mm plug wires and they all seem to be conducting fine. I pull the cap and rotor to find the attached pics show. I change those out for spares, throw in new NGK B4Ls and she’s purring. Recommended 1.5 ohm coil checked out fine on multimeter, FYI. I go for a short drive and this is how plugs #1-4 look after less than 5 miles. I didn’t pull the other side. #7 was always a little sooty, but never bothered me or the engine too much. My questions; What is going on with my cap and rotor? Could this be caused by high resistance after the plugs foul, or could it be the cause of the plugs fouling? Do the plugs look black because of oil intrusion? Bad rings or valves? My vacuum is steady at 19 mmHg (or however you write vacuum). No smoke. Again, good vacuum, good throttle response. Long story short; engine runs perfect until plugs foul and she suddenly begins missing terribly. What is causing the fouling? Your patience for reading all this is much appreciated. Thank you all in advance. Also, I just want to add that I really don’t think it’s the carbs or fuel related, but I could certainly be wrong.
Oh, also want to mention that I used one of those spark plug testers with the little light before changing the cap and rotor, and that showed that #4 was only firing sporadically. After the change it was nice and regular. Notice that #4 is not fouled, now, even though it was the worst when I pulled it. Fuel pressure is at 1.5 psi with a electric fuel pump and a regulator.
While no expert, I'd replace the cap, and look closely at the movement the distributor shaft makes, if any? You might do good to replace the rotor as well. Best I got for you.
Thanks for responding. Check and check. Replaced both, running great, but some plugs are sooting up real quick.
I agree with NoelC, the center carbon button on that cap is toast and the rotor has a big time evidence of excessive arcing. You are correct in assuming that the ignition system is going to try to fire the plugs if it can and it looks as if it just couldn't fire the fouled plugs. I would be highly suspicious why certain terminals on the cap look melted and damaged while others not. I would start over with plugs, cap, rotor and see what happens after about 10 miles.
As you pointed out, the cap and rotor, but when I see that I ask what's the top of the shaft is doing as well the bottom, there's got to be a movement to make that happen. Is there a bushing that's worn causing a wobble sloppy shaft whipping effect that eats those for breakfast?
Rain can make the ignition system do weird things, high voltage can find "ground" when things are wet. And condensation inside the distributor cap, caused by rain, can make it go nuts. I just wanted to let you know about that, since you sound like you might not be aware of it. The black stuff on the plugs looks like "rich" soot, not oil soot.
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