I just bought a 53 jeep cj3b with a problem I have never come up against. The back plug misses badly unless you pull the plug wire off and hold it just off end of the plug at which point it smooths right out. Snap back on and resumes missing again. Replaced wires and no change. Please help. Thanks
I have seen this problem when the spark plug is badly fouled. Having a secondary spark gap will allow the current to jump the primary gap at the spark plug tip. You didn’t mention replacing the offending spark plug. If that clears the problem for even a short while, you probably have a problem in that cylinder, i.e. excessive oil in the cylinder or coolant leaking into the cylinder.
Get back to us when you find the solution.
Once you take the head off, you might as well do a ring job and change the main bearings. Honestly, these things won’t always run forever with no maintenance. If you can remove the intake manifold, you might be able to scrape the crud off the valve. If the crud fills up the entire intake passage, it makes it easier to pull oil through the valve guide.
It’s either a fouled plug or a defective plug.
What you are doing when you hold the wire away from the plug will give it an extra jolt and then that plug is firing. I appears you need to replace that plug and if it is not new, you should replace them all.