I have one of these from six years ago (2-6-2, but really the same engine if you look at them). From what I remember, I ran the engine for a while to heat up the element that creats the smoke. Then I put one a few drops in there, four seems a little much for a cold start. It depends on the fluid you use, but try with smaller amounts, and as bob said, over use will leave behind some residue that you will have to clean off of your tracks. Don't use your smoke unit too long when you use it because it is housed in plastic which might melt when over heated.