SC Backfires

[Ryce Stallings]

I got my SC hot in traffic and it started to pop and backfire. I assume I vaporized the fuel. After shutting it down and letting it cool it ran fine. Today I drove it and at normal temperature it started to pop, backfire and then died.

Any ideas about what is going on? Air leaks, bad wires?

[timmy2]

Air leaks and/or bad wires are a good place to start.
Fuel pressures should be tested and mixture checked as part of the diagnosis.
CDI and coil as well.

[Orange911S]

The give away for me was when you said it ran fine after a cool down. This gives the coil time to close the gaps in the windings which causes the misses.

Here is an article that helped me sleuth this out:

What are the signs of a failing ignition coil? - Ask.com

Now for causes, my suspicion is that my bad set of plug wires contributed to my issue. Once I put in a new set of Clewitts from our host and a fresh coil the problems went away and haven't come back.

Jeff

[Walt Fricke]

An easy check to make is to pull the distributor cap and with your fingers rotate the rotor. In one direction it should move maybe 20 degrees. You should feel the springs which pull it back to 0 doing their thing.

If it sticks a bit, or hesitates so to speak, when hot and you start to move it off zero, you may have unwanted friction in your distributor's centrifical advance system. I had just this happen to me. Fine starting and idle hot or cold. But starting cold, engine would run fine (on the track) and after a while run very poorly off idle. If it handn't cooled much, would start back to its evil ways much sooner next time.

I pulled the distributor, pulled stuff off its side to get some access, sprayed PB Blaster in, used air to blow it out, did this several times, spun the shaft both ways at high RPMs by blowing air in at angles. Finally got rid of the sticking part. Sprayed white lithium grease in that lower part of the distributor (because I had it), put parts back on, etc. Worked great rest of event despite high 90s ambient. Distributor shaft was solid in its rotational bearings.

Just one more thing to check for. If the rotor can be advanced by hand freely, that's not apt to be your problem.

[Discseven]

Originally Posted by Ryce Stallings

pop and backfire.

Ryce, I recall my '85 doing this along with having very little power. Was DME.