Just bought my son a 50615 steam locomotive.  We can't get steam to come out consistently.  No instructions were included.  We added about 4 drops to the smokestack and ran for a couple of minutes.  Got one big puff and a couple of small puffs.  Added 4 more drops of oil.  No additional puffs after running for about 5 minutes.

3 boys staring at the train waiting for steam.  Please help.

Thanks.