As some of you may recognize, I have been using an a/f gauge to tune up my tired motor. Last weekend I was nearly there with rods and jets - a bit lean, but the car was running very well. I dropped from 43 to 41 rods to finish it. I then started the car and it now runs like crap - lazy on the revs, backfiring, sooty exhaust, etc... Figuring I dorked up the carb somehow, I put the 43 rods back in - no help. I then installed a known good carb (a new JET 800 CFM Stage 2) - it still does it. I had replaced all the plugs after a recent flooding episode. When I pulled #2 plug yesterday to inspect, it was completely oil soaked and wet, black. I put on a new plug wire for #2 and it didn't really help. I had already replaced the cap and rotor when I put on a Pertronix II electronic ign system.

I notice that the car spits gas vapor back up through the carb when I shut it off. It also holds a reasonable idle but spits and backfires when trying to get up to 25 or 30 mph. I have adjusted the APT screw on the JET carb (this is a late '70's carb with an access port in front of the choke tower to fine-tune the depth of the primary rods) to run richer... I would swear that this is like when you put a distributor in wrong and it is off by a big amount - but somehow the car barely runs. The problem is that I have checked and rechecked timing and it is good at 12 BTDC. Also, the vacuum advance can points to where it did when the engine ran well recently. So I now think that maybe my tired old engine has had the cam slip on the timing chain by a tooth. That would put the valve timing off and produce my symptoms - correct? What else am I overlooking?

At this point, I will drive the car up on a flat-bed trailer and tow it home to St Louis in a few weeks when I move back there. Too bad - I had wanted to drive it home on an 800-mile road trip...

I'll likely use this event as the catalyst to pull the engine and rebuild it...

 

Have you tried changing the O2 after all the fouling?

 

Did you run the plug wires correctly? Maybe you crossed a wire or two. Or improper adjustment of the valves.

Jim