225: bad ring or valve?

Back in December, the Jeep's motor bent a couple valves, and I recently got it back together with rebuilt heads and the rig is running a bit rough. This motor is a 225 odd-fire. It sounds and looks like it has an intermittent misfire, worst at idle, and still present but not as bad everywhere above that under light load/throttle. The entire ignition system is brand new (literally; key switch, wiring, ballast resistor, coil, points/condenser, cap/rotor, plugs) except for the plug wires, which tested okay and aren't that old. It has fresh valves, lifters, cam & chain, and I just rebuilt the carburetor (Rochester 2G) too. I did a compression test today, and all the cylinders were within 5 pounds of each other.

I've made an interesting discovery while trying to trace the miss by pulling the cap wires. There is little to no change in idle quality when I pull ANY of the even-numbered wires, and a noticeable drop in RPM and smoothness when any of the odd-numbered wires are pulled.

The needle on the vacuum gauge jitters between 17-19 inches, and every time a misfire occurs the range widens to 15-19, then starts to close back up again until another miss happens. It starts to pull smooth and steady vacuum at about 1200-1400 rpm. The idle mixture is adjusted as best I can with that (3 turns out), the idle is at 750 rpm, initial timing is at 10* with 34* of point dwell. I did the intake gaskets a couple days ago and used a fresh base gasket when I installed the carburetor, and I couldn't find ANY vacuum leaks with starter fluid, carb cleaner, or a squirt bottle.

He runs great, pulls hard, and has lots of torque, perfectly drivable. I'm just trying to figure out what this is because I just spent a thousand dollars on the engine and I want it running flawlessly. Two thoughts come to mind; ignition and carbretion.

Ignition: Is is possible that the contact point lobes on the distributor shaft are worn enough that the ridges are no longer precise? Is it possible that this is causing a weak spark on one side only, being an odd-fire engine?

Carburetion: I've rebuilt the carb twice since I've had it. The last time was just a couple weeks ago and I triple-checked the float settings before putting it all the way together. Is it possible that one of the venturis is partially plugged up with something, preventing the right amount of fuel from being drawn in, and that I missed it not once but twice?

Another thing that makes me think carburetion is that when I slam it wide open, it doesn't misfire at all, but instead lets out an absolutely gnarly growl and soars all the way to 5,000 and beyond. The misfires only seem to occur when the throttle input is constant and the engine isn't under much load.

When I pulled the plugs to do the compression test, the plugs on the odd side were black, like it was running much richer than the even side. The even side plugs looked good.

The engine visibly jumps slightly from side-to-side whenever a miss occurs, and the exhaust at the tailpipe feels normal except an intermittent "missing" pulse or two of exhaust. It isn't backfiring or afterfiring. Also, I can move the initial advance anywhere from 0*-12* and it doesn't affect the misfiring, however, it smooths out a little bit when I bypass the ballast resistor (sending 14v to the coil instead of 8). This is more noticeable off-idle.

I've been trying to solve this for about a month, and I'm stumped. Any help would be much appreciated.

Thanks!
-Tony

 

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