hi,i wondered if someone out there could help me.ive owned my 850t,1975,for 26yrs now,and re built it from a rat,my problem is when i start on choke i have a backfire it seems to go when warmed up,i had electronic ignition fitted and want to know wether i need to change the ignition coils,or could this be a fuel broblem? id be very gratful for any ideas, cheers paul d