A while back I posted a thread about getting an ignition coil for the car in my signature. Now I have a bit of a long story and a problem that I haven't been able to solve. At the risk of sounding like a moron, here is the saga. I apologize in advance for the novel that I'm about to write. I have been waiting for a water pump gasket to replace the water pump because the one I have now is likely the long style and the belt squeals at higher rpm. The old water pump didn't cause a squeal. So I decided not to change the coil until I had the water pump gasket so I wouldn't have to tear apart the area twice. So, in the meantime, I changed out the cap, rotor and spark plug wires with AC Delco parts. I had it all nicely routed and the wires separated and engine fired right up and ran really well, I even had to dial down the idle on the 850 Holley double pump carburetor. I took it for a test drive and all seemed well, there was just a bit of a stumble as I let off the gas for a sharp bend in the road. I didn't think much of it because the car ran fine otherwise. The next day, I took it for a little drive and all seemed fine again. Then I decided to take it to my mom's place where there it a hoist as I was planning to change the steering idler arm. On the 10 minute drive to get fuel, the car started to stumble and give little backfires through the exhaust. I stopped on the side of the road and made sure the connections of the spark plug wire as the coil and on the plugs themselves were good. It started up fine and ran fine. I got fuel without incident and continued on the half-hour drive to my mom's place. About 10 minutes later, the car let out a backfire that blew the passenger side muffler apart. I shut the car off, checked to make sure the connections were good and decided to limp the car home. On the way home the car continued to give little backfires and it kind of felt like something was lifting back on the gas pedal. It feels like that every time it starts to stumble and backfire. It just about quit and backfired, so to try to avoid internal engine trouble, I shut the engine off. The road was a country tar-and-chip road with a pretty big crown on it and the car immediately headed to the ditch. I tried to turn the key to the "on" position, but with me trying to turn the wheel, the key wouldn't turn. So...in the ditch I went. I thought for sure I was going to roll over because the ditch was steep. Luckily, it stayed on all fours and I was able to get it towed out of the ditch without any damage to the car and thanks to my Hagerty insurance I got it home on a flat deck tow truck. Anyway, the car will start and run. Usually when it gets warmed up, it will stumble and almost quit, other times it will stumble and die. It usually idles well, and then stumbles. I have since removed all of the new ignition parts and re-installed the parts that were on the car. I have checked fuel pressure with the engine off and it's right around 6 psi. I have pulled and cleaned the plugs and I have done a compression test. All seems well there (the lowest is 140 psi[#1, 4 and 6], the highest is 150 psi [#2] and the rest is 145). The test was done on a warm engine. I've changed the coil wire and one plug wire that had crack in the jacket. I have taken it for a drive one day and was up and down the road a half-dozen times each way and all seemed fine. I decided to take it home because the car is pretty loud with one blown muffler and I didn't need the cops to stop by. The next day, I took it out again and I barely got it home after the first trip up the road. It has been running really rich and when I pulled the plugs, they were black with soot. Today, my brother and I worked at it (he's a pretty skilled self-taught mechanic), but again it was running great in the shop, but the first time I went to take it for a road test, I didn't get out of the laneway before it started its old tricks. Then we tried it again and it went up and down the road seemingly fine. I brought it home and shut it off. When we went to go for another road test, the car would barely start and the carb was dumping fuel into the intake. When we started to look at it today, the clear plastic fuel filter was empty. My brother wonders if the Stage 1 mechanical fuel pump is on its way out. Could it be the Mallory ignition box? The coil. It seems to really act up once it is warmed up. I have attached a video of the car idling and stumbling. I know it's really difficult to diagnose a problem without being there in person, but I'm frustrated and desperate. The really frustrating thing is that the car was running fine before I attempted to "improve" it. I guess the old addage "If it ain't broke, don't fix it" holds true. Again, sorry for the novel. Any help you can offer is appreciated. Here's the YouTube link:
You replace the good parts with bad part check the cap, rotor , plug wires The coil either works or it doesn't. What ignition are you running ?
Backfiring in the exhaust is usually a result of cross firing, which is much more prevalent with fuel fouled plugs.
The video was taken after I put the old parts back on the car, that’s why the red Accel wires are on there. It is a Mallory ignition that replaces the points in the distributor. I have checked to make sure the wires are correct and when I had the Delco wires on it, I even made extra looms out of zip ties. I haven’t changed coil yet.
Check connections and make sure all coil wires are not loose. BASICALLY, it runs fine cold but not warm?
Should I try larger diameter plug wires like the MSD Super Conductors to try to eliminate cross-firing?
No, your problem is not the spark plug wires. By cross firing, I meant with fuel-fouled spark plugs, the spark would rather jump to another cap terminal and fire a spark plug that’s fouled and not under compression, hence the backfire in the exhaust because the spark is jumping to a cylinder with an exhaust valve open. KV requirements to ground on a fuel-fouled spark plug not under compression are much lower. Electricity follows the path of least resistance. It seems to me that you have a strange ignition problem, or the carb is flooding.
Also check your distributor cap alignment. There is a small tab on the inside edge of the Delco cap. It fits into a notch in the distributor body. Just make sure the cap is on right. It is possible to overlook this, and it will cause back fires like you are describing because of cross firing. Take the cap off and look for the tab and notch. Make sure they fit together.
Have you checked the float levels on the carb? Have sight glasses? Sounds like high....that's why OK till warm.
You've got carb issues. I'd guess it's so rich it barely wants to run. But you ought to do normal diag stuff before guessing. Check for vacuum leaks, verify the firing order, check and set the timing as needed. Then look at the carb.
I’ve done a fair bit of investigating this. I burned nearly 3/4 of a tank of fuel messing with it. I had to add some of my lawnmower gas instead of heading to town with a Jerry can. Not long after that, the car started to behave better. I’m pretty sure that a crappy batch of fuel was at least part of the problem. I have also installed the new mufflers so I can actually hear what’s going on better . I re-torqued the intake manifold bolts, reset the floats in the carburetor, installed a new primary needle and seat on the primary side, even though the old one looked fine. Yesterday, I reinstalled the new cap and rotor. I’ll reinstall the new plug wires later. I want to go one step at a time to see if I can pinpoint the problem. It ran well with the new cap and rotor back on, so I drove it a half-hour to my folks shop (it has a hoist) to get rid of a header leak just because it was bugging me. I used Remflex gaskets after readzing great reviews of them here. My next step is to reinstall the new wires and see how it runs after that. I also discovered a big vacuum leak at the brake booster where it meets the master cylinder. I’m currently awaiting a new seal for that. Once I change the seal, then I can move on to tuning the carburetor better. Last night it ran better than it has since all of this happened. It’s not perfect yet, but with any luck, it will continue to improve. I’ve driven this car all over the central and southern part of this province, it’s quite a thing to not trust it to go a couple of miles without issue. I’m not used to it and I sure don’t like it. Last night was encouraging, for sure. Thank you for your input and suggestions. I’ll keep you posted on my progress.
I was going to suggest a substantial vaccuum leak, so good to replace that seal. This sounds like issues I've had in the past inside the distributor - I would look there for things like a worn [whatever that little bronze contactor thing inside the top of the cap that rides on the rotor is called], as well as looking at everything else inside the distributor to make things are all acting correctly. Did the rotor come loose? Is the vacuum and mechanical advance working freely? (Any broken advance springs?) -Bob C.
Everything inside the distributor looked good, just dirty. I used some electrical parts cleaner to clean things up.
I went through hell with mine. Ran a big red 12 volt wire from the fuse block to a resister, then to the coil. Never had a problem again. The stock factory resister wire to the coil can go bad. Causes missing and shut down.
