VCCA Home Forums GENERAL DISCUSSION New User Forum carbon fouling plugs/rich mix

Good afternoon, I have a 1950 Chevrolet Styleline Special that has been in the family since new. I have always been the one to take care of this car and have seldom had any problems. Probably over a year ago I began to have issues when I tried to drive at low steady speeds (I have a standard 3 speed) that I would call random bumps, as opposed to a miss. I have tried lots of things in the process of just making sure the engine was as to spec as possible. The 216.5 was rebuild about 20 years ago, has about 5000 miles since then and is very well maintained. I list just a few things I have done: electronic pertronix ignition, new ignition wires, new dist cap, distributor was bench tested and set to original specs, just had the carb rebuilt to spec from a proven carb company, new fuel pump, has a clear bowl on the fuel pump and at the carb both of which are clear, and new plugs. Just got the rebuild/speced carb back and was sure that the Carbon Fouling plugs were due to too rich a mix and the carb rebuild would take care of that issue. Unfortunately it did not. With only 10 miles on a drive, the car bumped randomly about every 5 seconds if I drove steady state in any gear and the plugs had black dry fouling. If I accelerated hard, it took off strong. I still believe it is bumping due to only a partial burn because of too rich mix. I checked the vacuum and it was over 16 which is good and normal for this car, so I don't think I have a vacuum leak. Anyone have any other suggestions? Thanks much, I am at a loss.

Just some ideas to consider.

With only 5000 miles since a rebuild I would expect higher vacuum, maybe more in the 18 - 19 range. You might want to keep checking for vacuum leaks. Remember the hose to the wiper motor when checking.

I assume it is manual choke car and that the choke cable to adjusted properly.

One other item to consider is the electronic ignition unit. Typically they fail completely and suddenly but there could be a pending problem. I assume that whoever set up the distributor also properly set the gap between the reluctor wheel and Hall effect sensor.

Also make sure that the heat riser valve is opening completely.

I remember having a similar problem on a pertronix equipped motorcycle. If battery voltage started getting low it would stumble and eventually quit. Maybe yours isn't getting to the quit point, just the stumble.

Dave

I agree. Get rid of that stupid Pertronix....that electronic system causes nothing but problems. Also, at idle and in neutral your vacuum reading should be in the range of 18 to 19.

Thanks Rusty for the quick reply. Wiper motor connection on the manifold is plugged. Choke is set correctly. Timing is right on the dot. Yes, I have questions about the Pertronix since it is hard to know if it is working correctly, and went through this exercise previously swapping back to points and back to Pertronix. The heat riser is operating correctly. I assume the distributor is set right since it was someone who does it as a business and has the equipment to test for proper advancing of the mechanical and vacuum advancing.

Thanks Junkyard Dog. Had Pertronix once and went back to points. Got some new points and condenser and the condenser was bad. Decided to try Pertronix again. If I could just verify where the problem I would be happy to pick one or the other. Maybe I will go back to points again and give it yet another try.

Definitely give the point system another try with a known good condenser. The point system is fool proof and easy to work with. Also, the points can be replaced along side the road.......the stupid Pertronix can't. I had Pertronix on one of my cars and it lasted a week before it failed and left me stranded right in the middle of traffic on a major boulevard in town. At any rate, go back to the points system and if you still have the same problem look elsewhere. At least you will know that the problem isn't with the points.