The spec is .75/80degree solid(B). The furnace calls for B (solid), but as a low flow (.75gph) I tried the A (hollow) looking for a solution. . The A type nozzle is what worked for the past year. Then I ran out of fuel, filled up the tank, let it settle, changed the fuel filter and nozzle with the correct nozzle 75/80B and restarted the furnace. A donut sized carbon ring appeared in 1 week after replacing with a B, shutting down the furnace probably because the light sensor couldn't see light, so I went back to the A. It lasted a day and the same thing occurred. The problem is not nozzles at this point.
sorry, nothing has moved. it is all very rigid.
I siphoned contaminents from the bottom of the oil tank, changed the filter and nozzle once more and it is running. There was algea of sorts blinding the filter, and that restricted flow, and caused the problem. The furnace is now running normal for 3rd full day. This issue is closed. I did not accept your answer.