This is a somewhat old picture. It has a petticoat now but it’s an exhaust adapter cut down to the flare and wrapped around the outside of the petticoat pipe. I think that the steam is catching the bottom of the petticoat pipe inside of the petticoat and causing a problem. I’ll try to get an updated photo. Even on air it steams fairly poor. The boiler should be pretty clean as well as the flues. The grates are in good shape and there’s a fair amount of room around the top of the ash pan to let combustion air in.
looks to me like your blast nozzle and your blower ring are sitting too far down in the smoke box.
The rule of thumb is that your nozzle should be about 1/3 of your smoke box, the petticoat should be about 1/3rd, and the middle 3rd should be open. What is probably happening is that your blast from your nozzle and your blower ring is not being completely contained inside the petticoat pipe.
Another thing to check on, and this is really important... Make sure there are no leaks inside the smoke box or between the smoke box and the boiler. If there are any, it will draft very poorly. I've dealt with that before, and if you have a leak, it really doesn't matter how good your nozzle/stack is set up.
Segue? This locomotive is a variation of the camelback built on the MERCER A5. I bought it in its current configuration and it didn’t come with prints. I was hoping that somebody that’s tackled this variation could lend some expertise.