Technical

I have just taken my Flying Scotsman out of the box after quite a while and followed the video procedure on starting up. I can get the loco to go using right clicks on the valve controller but clicking left doesn’t work to slow it down. The only way to stop is to hold the controller right over as long as it takes to get a red light. This is the same for either polarity of the supply. On removing the body and looking at the valve motor I see it takes a few revs on each right click but only a partial Rev on the left click. Also holding left doesn’t operate the valve motor continuously. Any ideas?