Have a 2002 Lionel Blue Comet, did the modification Lionel recommended a few years ago. The unit puts out a good amount of smoke but about only about 60% goes up the stack, the balance wafts out under the boiler. The screws on the fan unit are tight, the gasket is in place and the fan seems to run properly. Seems like the fan is not pushing the smoke out of the stack fast enough. Suggestions deeply appreciated.