i dont mean to question ur intelligence or the intelligence of the mechanic
but make sure its running well carby/intake wise.. running to rich or lean will be blocking out different plugs all the time..
without having to go in depth to check urself..
replace all the plugs, or atleast clean, and if it doesnt run any better than intake is out of the question, if it runs great for a minute or so, then yeah, running too rich or lean