i had one years ago that used to do that ,and it would puff out white smoke and come to a stop !

it turned out to be dirt in the tank! but when i converted it i did remove the guase on the end but it was like black piant going up the lines! took the tank off cleened it all out and it was as sweet as a nut after that, on my lovely brand new york engine that was old stock in the box from fords for £200

they were the days!
oh and before somebody says there is no such thing as a good york you are wrong!
