Barry, This may seem a bad idea but here goes anyway. If you are restoring the engine does that mean you are taking the boiler off the engine?, If so, what would happen if you gave the boiler a bath in pickle then gave it a good hose out with water. Would it not clean the tubes up or at least soften the carbon to the point where you could use your flue brush again. Regards, John MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.