Hey fellas, I signed up here several years ago and never really posted much other than an introduction... I'm tinbender's nephew, and here I am with a thoroughly perturbing problem begging for advice. I have a '69 Jeep CJ5. His name is Wilford and he's absolutely indestructible. Back in December, the 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 Buick 225 odd-fire V6. 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
Alright, I did some research (and by research I mean I looked in the Haynes manual) and discovered that I mis-remembered what the dwell setting needed to be. It's supposed to be 30*, not 34*. I got the dwell set correctly and it's running MUCH better. It's still got the intermittent miss, but it's much less frequent. I'd say down to about 20% of what it used to be. I noticed when I had the dizzy cap off that the points were a bit dark. They didn't seem to be pitted, just a little blackened. There are about 1000-1500 miles on the points, is this a normal amount of wear? This is also much more smooth. It has a mild cam, so I'm not expecting it to be perfectly steady at idle, but it's jittering between 18-19 inches now, and only widening up to 17-19 when the miss occurs. I didn't have any sandpaper or an emory board at the time, so I just set the timing and idle mixture and closed it up, but I'm betting if I were to clean the points up a bit that miss would go away completely.
Alright, problem solved. I'll post what I found in hopes of helping someone else someday. I moved the dizzy one tooth clockwise, moved the wires over on the cap one space, and it's running smooth as butter now. I thought about it... since the odd-firing pattern is 45-75-45-75-45-75 instead of the even-firing 60-60-60-60-60-60 (like would be found on just about any other 6-cylinder), and it had a weak spark on a whole bank, the points and the rotor had to be off from each other, if that makes sense. Basically, the points timing and where the rotor actually was were off. This isn't a problem on an even-fire engine, but on an odd-fire, if the points are not on the correct set of lobes for the set of three cylinders (one of which receiving the spark at that moment), you get a spark pattern that doesn't go with the timing of the rest of the motor, which is exactly what I had. It's generally running smoother, with almost no vibration at all, ease of starting is 1000% increased (you don't even need to choke it to get it to start, two pumps and it'll fire instantly and idle pretty smoothly at about 400 rpm. Choke will bring it up to about 1000 when completely cold, when warm it sits right at 750 until you tell it otherwise), got a noticeably increase in power, better power delivery, and I'm sure it'll help the fuel economy.
Well, on the Prestolite distributor (mine) the cap towers are evenly spaced but the rotor contact is elongated: http://www.oreillyauto.com/site/pi/detail.oap?line=BOR1&item=C203 http://www.oreillyauto.com/site/pi/detail.oap?line=BOR1&item=D180 The rotor was on the right cylinder, but the spark was happening 30 degrees before or after it should have because the points were on the wrong set of lobes.
Suddenly found your post today. I got exactly same probmlem on my 225 cid V6 on my A-Coupe. I moved the distributor one tooth clockwise and moved the wires over on the cap one space just like you did. Ta-daa!!! Engine is running smooth and got much more power and torque than ever! Thanks!!!
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