You have probably already been given the right answer. But before tearing the whole unit apart, I would check the regulator valve orifice for contamination. Usually if this is plugged up, the lift quits completely. But it is worth checking. The regulator valve itself may be sticking as well, but that gets you into the total overhaul situation.
To check the orifice, you will probably need to remove the gas tank or the instrument panel, more likely both. You will find a pipe plug screwed into the Touch Control head. remove it and you then have access to unscrew the orifice (which should have a screen attached). Clean the orifice and screen and put everything back together. With luck, that may fix it.
If you get into anything more involved than this, you should get a copy of the Blue Ribbon Service Guide for Touch Control from Binder Books http://www.binderbooks.com
. You can also find it on-line at Rudi's manual server (link on Rudi's posts).