i printed out the article yesterday night! thank you.
I checked timing again and did some work on it, by setting the initial advance to 10-12 degrees i get a total of 44 with bith mechanical and vacuum,i thought was too much so i tried to disconnect the vacuum one...result is that mechanical only advances 16-18 degrees so i'm reaching 30ish at 4000 RPM wich is too much.
Reading the article on cranckshaft coalition, they say advance can go up to 45-50 during light throttle cruise with no problem getting a better fuel mileage and a cooler engine, i'm not considering mileage like the goal, i just want to solve this problem and a healthy engine, fuel mileage is a bonus.
I' ve got new spark plugs 10 minutes ago, they're colder than the previous Accel, i hope will help.
Another thing i noticed driving the car is the misfiring happens just if i push down the pedal all the way suddenly but not if i rev up the engine gently, guessing is a good clue for you, i'm thinking about too much fuel and a denser mixture in the combustion chamber coupled with a too hot plug that cause preignition?