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Well I broke down again today but in NJ. Weather was nice, about 75 F. Car running cool at about 180-200 F. I had the car trucked from Miami to use this summer in NJ. It runs cool in Miami too, 180-200, even in traffic. . Over past 6 months the 1972 C3 with 350 engine, 4 spd (46k miles), burned out 3 electronic ignition modules and coils. Failure was traced back to a faulty alternator. Also three batteries! Now it has points and condenser. Drove 1000 miles in Miami in hot humid weather and it drove fine. Now its stalling, bucking again but not totally dead like in the past. Previously when it got hot (30 mins of driving) it would stall and not restart until it was cool and backfired out of the exhaust like a machine gun ! I had ruled out vapor lock using a thermal gun, all lines and fuel pump are reasonably cool. Car has new vintage air kit, electric fan, new headers replaced the stock manifold, new fuel pump, filters, clean tank, new hoses and lines all around, new PS and Wilwood brakes/booster, new cap, rotor, points, condenser. I am starting to think the carb or carb float or vacuum advance is now messing up as its not exactly the same symptoms as before (when the ignition module/coil fried). After stalling today, it restarts but its running slightly rough and can hear small backfires in exhaust when pressing accelerator pedal, also I am hearing much more small backfires from the exhaust upon deceleration. I hate breaking down and so maybe I look for the cause but to be safe replace the wires, plugs, and replace/rebuild the carb. I also recently noticed slight blue smoke on cold starting so I suspect the valve guides are going. But I dont think this is an internal engine issue. Beyond that I am stumped what it could be ? Any help or ideas welcome. Stan
Your plugs could be the problem if they are oil soaked. Pull out a few and check. Your valve seals may be bad, most likely not the guides. How is the timing, dwell etc. ? Put a vacuum gauge on the engine and see what it reads. Jerry
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
How old is the timing chain? you could have jumped a tooth or two. Just verify your top dead center with a piston stop and then compare it to your timing mark. It will rule a out a major issue and get you closer to your solution
Check the fuel filter(s).
Run a can of SeaFoam through the tank.
Could be a float or fuel level problem.
Triple check your ignition.
I recently got rid of a sleight miss that was worse when the engine got hot, that has troubled me for a couple of yrs.
Over time, I'd replaced the points, cond., cap, rotor, wires, plugs. Checked the timing.
Didn't solve the problem.
Then it developed a rough idle a few months ago.
The SeaFoam in the tank solved that.
I recently bought a new, AC Delco dist. cap, the good one with the copper inserts.
Problem solved.
The old high quality cap with copper inserts looked good (not GM) but I was grasping at straws, and grabbed one that worked.
Thanks will try seafoam. Nearly all under the hood parts are new and seem to function fine.. its a gremlin! Will check vacuum and timing advance. thank you again,
What kind of ignition coil do you have? Have you checked coil primary and secondary resistance, especially when hot? Without knowing what you have, I would say primary should be about 1.5 ohms, and secondary about 8.5K to 10K ohms. One other item, when you switched to points did you add the resistor wire to the coil to reduce the load on the points? Also. point dwell should be 28 to 32 degrees.
Last edited by Mrvettenick; Aug 6, 2021 at 06:59 PM.
Thank you , I have been remiss in checking this before , e,g, ohms..I will check today. I had the coil changed 4 times so now I am confused on what I have on their now but I know I did have 2 flame thrower coils before. Going to see my mechanic today to sort this out. Much appreciated. On retrospect, when I was 25 I had all the equipment to do this ( was a pretty good mechanic). Now at 57, and in medicine for years I got lazy and just let the mechanics sort it out. After this crazy last 6 months of breaking down no less than 5 times in Miami and NJ ( and thousands of dollars later) , I am going to have to take this into my own hands and check out the details. Pissed that even so called Vette expert shops in Miami missed so many of my original issues, e.g. bad alternator.
Stan. you don't have to make any excuses or justify what happened to us. We're all in your corner. Hope it gets solved soon. If not, let us know. we'll do our best.
OK, changed the plugs ( NGK). When car was cold it runs great. Drove 40 mins on highway ( 85F here in NJ). the car started to stumble, sputter about 30 mins in and ran rough and hesitated, slight bucking. While all the mechanics swore the wires were fine I decided to pull a few when I arrived home with the engine still stumbling. With engine running, I pulled #1 wire and there was no change in the rough idle at all. ... hmmm... So i checked the wire for spark, and Nothing.! . Then pulled #3, it had a good spark. Here is a photo , It has a napa coil that is asking for a 903 external resistor... I cannot find the external resistor ( Napa 903) , where the hell can it be ? The coil was super hot for an hour even after stopping the engine. I assume this is because improper voltage into the coil. OK so seems to me the people that worked on in screwed up the resistance wire ( not connected and just dangling in the air) and there is no external resistor on the coil to be found. ... comments welcome. My neoghbor told me to just convert to an MSD unit 6L ? Are MSD better ?
Also the car was running about 15 F hotter than usual, coil with resistor wire hanging off... and i cannot find any external resistor
yes ordered a set of wires and also going to replace the coil and figure out how to add the resistor. While I have to check the voltage, it appears to me that the coil has been receiving 12 v all the time and probably why it is so freaking hot! you can cook a chicken on it after just 40 min drive.
That white braided wire is your resistance wire. Is it attached to the positive or negative coil. terminal. Since it appears that your issue arises when hot, leads me to believe that it's a too high float level, or a coil crapping out.
When it acts up. turn it off and look down the carb throat. If you see fuel getting into the throat, then your float level is too high. If you see nothing, then check primary and secondary coil resistance.
Thank you... I think this the coil.. Just tested the resistance wire... no voltage at all. dead..and the only wire they had connected seems to be a 12v continuous. So now looking to correct the resistance wire , new coil. Points look OK. As the carb is original I believe I will change that too. I am amazed at the incompetency of my mechanics.. I know just enough to be dangerous but as a scientist I can dope things out. Thanks to all for you help.
Thank you... I think this the coil.. Just tested the resistance wire... no voltage at all. dead..and the only wire they had connected seems to be a 12v continuous. So now looking to correct the resistance wire , new coil. Points look OK. As the carb is original I believe I will change that too. I am amazed at the incompetency of my mechanics.. I know just enough to be dangerous but as a scientist I can dope things out. Thanks to all for you help.
Slow down. Before you spend some money, just run those tests I mentioned. Let us know what you find.
C3 stalling and bucking issues
