Riello 40g fire up problem

Hi i'm hoping someone might be able to help me,my gas oil burner is for a automotive spray oven,the problem i'm having with it is after the air damper has opened on start up when it fires up its what can only be described as quite violent as if its over fuelling and flashes come out of the air damper opening,it does fire but smokes really bad and the fuel spray seems like its fluttering,when i take the burner out to check it again its really black with traces of un burnt fuel.
I have changed the coil on the fuel pump,the photo cell and the electric control box,its a 530se model. But its no better,i was thinking of trying a new nozzle,it has a develan 2.00gph, 60deg w, can anyone help as i've run out of ideas,any advice id greatly appreciated,cheers

Also forgot to say i tested fuel pressure and its bang on what it should be for the nozzle,thanks

Your symtoms indicate late ignition, this is caused by the ignition electrodes not set at the right gap or set to far behind the nozzle. It can also be caused by the spark occuring elswhere by the electrode leads insulation breaking down. Check the burner set up instructions and adjust the electrodes accordingly. The other possibility is that the nozzle is worn or the pump pressure is to high causing the flame to blow of of the end of the nozzle

spraggo said:

Your symtoms indicate late ignition, this is caused by the ignition electrodes not set at the right gap or set to far behind the nozzle. It can also be caused by the spark occuring elswhere by the electrode leads insulation breaking down. Check the burner set up instructions and adjust the electrodes accordingly. The other possibility is that the nozzle is worn or the pump pressure is to high causing the flame to blow of of the end of the nozzle

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Hi thanks for the reply really appreciate it,got a new nozzle and eclectrode today, fitted them and set it all up and worked for a bit but still smoking then same problem occurred.
So i thought i would take the side panel off to check the flue,and i couldn't beleive what i saw,every tube was fully blocked with black soot and all the internal chamber,so much for the so called service i had done 18months ago,it doesn't get used a lot so obviously he never bothered cleaning this out.
It took me 2 hours to clean properly,a seriously messy job i looked like a miner by the time it was done.Put it all back together and everything is running 100% fine,no smoke perfect fire up everytime,i'm really pleased,in future i'll be cleaning the flue every 6 months to keep on top of it,cheers