im having a problem with my so76 i just got to restore it has been sitting sense the early 90s started checked out motor and found no fire to the plug after some checking found the condenser for the points was bad so installed and electronic ingition on that bypasses the condense i now have fire to the plug took carb apart and cleaned was fairley clean for as long as it has been sitting cleaned all the jets and passeges and put back together and got fuel to the cylinder but whwne you try to crank it is backfires through the carb and some times it back fires throught the muffler checked the aluminum ket in the fly wheel and it is ok what am i missing please any info may help