Turbo 10 wood burner Dampers

[gordon_s1942]

I have a fairly old 2nd hand Turbo 10 tiled wood burner and the way its going I think the Cold Air isnt entering the firebox properly.
I remember seeing advertising material for these and they showed how air was circulated around the firebox as a 'preheater' before being burnt.
I have checked the top damper to ensure its opening and I dont think the chimney is restricted because with the door open, the fire picks up straight away.
I have looked around the net, checked installers who sold similar but no one now has any details of this particular style.
On the right hand side when facing the fire, there is a small lever that connects to rod that goes under the heater but to where and does exactly I dont know but moving it doesnt seem to make any difference and it weighs a ton to pull about anyway and certainly not this time of year when the heater is needed.
With half way decent wood it should burn hot enough to melt the paint off the wall but currently its flat out defrosting Ice Cream.
I would appreciate any info on this heater.