miller hot air problems

heatmiser

recently got a bad nozzle in  miller hot air furnace. the furnace had run that way for a while it was full of soot. changed nozzle,cleaned out roof jack etc still have a positive draft over the fire.is there an easy way to clean out the flue passages without ripping the whole furnace apart? any help would be appreciated

billtwocase

only one way

clean them is to start dismantling