I saw that you tried to retarded the timing, but that is the wrong way. Retarding the timing will only make it worse. As I said in post #6, advance the timing a few degrees (4-6) and see what happens--that WILL help but be sure to drop the idle down to specs after doing it. Just don't advance it so much that it pings or the starter bogs when the car is hot.
SERIOUSLY--it costs you nothing to try.
SERIOUSLY--it costs you nothing to try.
From The Secret Life of Spark Plugs {LINK}
Different lengths of insulator nose result in varied characteristics and different heat ranges. Heat is dissipated from the insulator nose through the center electrode and the inner seal ring to the spark-plug shell. If the insulator nose is long, the heat-transfer point formed by the seal ring is further away from the hottest point on the insulator nose than with a short one. So it follows that spark plugs with a long insulator nose can absorb more heat than plugs with a short insulator nose.
Quoted material is on page 4 , the section starts on page 3.
Part of this is I have my doubts the plugs are glowing hot enough to diesel,
But I'm even more doubtful an engine with 6k miles has caked on carbon deposits.
Some say advance timing, others say retard the timing, some say set it to idle rich, others say lean. aparently there is no clear cut answer.
I suspect the real problem is the fuel. Is there a carburator installed on any consumer vehicle these days? Hell no. Engine management corrects for 'bad fuel' and when power is removed the injectors just don't pass fuel so no run on.
You could have gotten a bad batch of fuel. Or your using fuel from the wrong refiner, back in the day some people would swear by Sohio/Boron/BP, others swore at it.
If you go to a colder plug and the problem goes away you have found the ignition source, unfortunately you then have to find a plug thats hot to self clean without dieseling.
But I'm even more doubtful an engine with 6k miles has caked on carbon deposits.
Some say advance timing, others say retard the timing, some say set it to idle rich, others say lean. aparently there is no clear cut answer.
I suspect the real problem is the fuel. Is there a carburator installed on any consumer vehicle these days? Hell no. Engine management corrects for 'bad fuel' and when power is removed the injectors just don't pass fuel so no run on.
You could have gotten a bad batch of fuel. Or your using fuel from the wrong refiner, back in the day some people would swear by Sohio/Boron/BP, others swore at it.
If you go to a colder plug and the problem goes away you have found the ignition source, unfortunately you then have to find a plug thats hot to self clean without dieseling.
Your timing seems too low based on everything I have ever read about what Ford small blocks like. Should be in the 12 to 16 degree initial timing based on engine mods etc. Have you tried bringing it up to 12?