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1966 390 engine missing/dying when gets hot

Discussion in '1955 - 1966 Classic Ford Thunderbird' started by rebel7254, Feb 5, 2019.

  1. Has Pertronix electronic ignition. Don't know if I, II, or III type. Runs great until gets hot 15-30 minutes, then starts cutting out and sometimes die. Sometimes can give it more gas and it will keep going but start over again. Any suggestions? Have had trouble with Pertronix ignition in my 1965 Mustang 289 fastack; had to replace twice.
  2. I would contact Pertronix since you have two cars with problems
    rebel7254 likes this.
  3. If you're certain that your problem is ignition related, check the ignition. I have a Pertronix and it's wonderful, but if you feel you have a problem with it, look in that direction. Bad coil? Don't overlook the wires and distributor cap.

    That being said, there's a known common problem with heat-related rough idling and stalling that's carb related. I believe your original carb has a spacer plate. I have an Edelbrock carb and manifold, and had this problem really bad until I bought a spacer plate to install under the carb. Big improvement, still has done it when it's hot out, but after a good radiator clean, the motor runs a bit cooler and this issues seems to have disappeared.

    The issue has to do with the gas -- it's now an ethanol mix, which has a lower boiling point than straight gasoline. The combination of this, plus the carb getting a little hotter than it should, add up to gas boiling in the bowl, causing rough idling, stalling, and even a gas smell after shutting it off. It's at its worst if you stop at a store, then get back in the car to try and start it., It's tough to back out of that parking space!

    Something to consider!
    rebel7254 likes this.
  4. I put in Pertronix 7 or 8 years ago. The Pertronix ignition works fine but I have had to replace the coil twice. I also had the carburetor rebuilt and then finally replaced it 1 1/2 years ago. I also only use non ethanol in all my collector cars. No problems then. I have a friend that has several collector cars and he uses fuel with ethanol and is always having problems and when I suggest that he switch to non ethanol he tells me he doesn't believe that is his problem.
    Also check to see if the hose from the radiator is hooked up that goes to the carburetor base. This heats the base but also prevents it from getting too hot. That hose then goes to the heater. If you have AC then I am not sure if that is still true.
    rebel7254 likes this.
  5. Thanks. Will check into these. Always use premium non-ethanol gas.
  6. Thanks.
  7. I have a 66 .. 390 with Edlebrock carb … same issue, back firing out the tail pipe. Carb is set up well and I was told it could be a fuel pump issue, not enough fuel getting to the carb. I am thinking of switching to an electric fuel pump … anyone done that and what is required .. and idea's on a brand of pump - 7 to 9 psi, at 40 gph. And would I need a return line?
  8. fordrodsteven

    fordrodsteven Well-Known Member Gold Donor

    I don't know a lot about Pertronix systems but I used to be pretty adept on carburetion and the old point / condenser type ignitions when I was young. On one car I found the condenser was bad. It would get hot and not function properly. The car would backfire and have very poor acceleration when I stepped on the accelerator pedal and when I let off the gas it would smooth right out and run perfectly. Another car I had would accelerate poorly and run okay (not perfect) at idle. I was setting the points / dwell and noticed that it would not settle down and hold setting solidly. The problem was the breaker plate inside the distributor was broken away from the pins that it rotated on. Another car would constantly misfire under acceleration no matter what I tried to fix until I noticed the bare wire inside the distributor that would hit the side and ground out the ignition system when the breaker plate would move to advance the timing. The one time I did have a carburetor problem was because the power piston (accelerator pump) in the carb was so worn it would not give the shot of fuel to the engine when I stepped on the accelerator pedal. I first changed the fuel pump thinking that was the problem but then had the same problem with the car even with a new fuel pump. The car would run great as long as I didn't accelerate hard. If I made a hard acceleration it would stall and then take me quite a few tries to get it to start up again. Once running it ran really good around town until I stomped it again.
    So based on the percentages of my past experience I usually look toward the ignition system. Usually carburetors tend to worsen over time and a problem kind of grows worse and worse. I find with ignition issues the problems sort just suddenly appear and sometimes are very difficult to find if you don't troubleshoot properly. You need to consider ALL aspect of the cars behavior during the different processes of driving a car. Does it back fire only on acceleration? Does it backfire only under deceleration? does it refuse to idle smoothly? does it lose power under certain conditions? Is the timing set properly? Is the vacuum advance working?
    My best guess with both the cars mentioned in this thread is that their problems are most likely ignition related and you need to narrow down what could be wrong using standard troubleshooting procedures and tools to find the problem.
    On both of the cars mentioned in this thread, if they don't have points / condenser, I would be checking the coil first.
    Last edited: Feb 17, 2019

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