Choke Sticking On: Often the choke sticks on, for no apparent reason. The throttle cable is sometimes too loose to pull up the choke trigger. More often, the choke trigger lever has become bent or twisted. This happens often because great care must be taken to keep the trigger against the side wall when the top assembly (throttle slide, choke trigger, cover assembly) is installed. Before the top screws are tightened, and with one finger holding the top in proper position, it is wise to test the choke by directly pulling on the throttle wire. It should click off at full throttle. Only then should the screws be gently tightened, while holding the top with that finger. If not, then inspect the trigger lever for misalignment, and re-align carefully with small pliers. Sometimes rounding off the side edges helps the trigger lever to not stick also. The last resort is to replace it, but pushing out the tiny hinge pin is difficult. So it is better to straighten it.
Here is the engine side view of a Delorto SHA carburetor. At the base of the vertical brass “spray tube” with one or two holes in it, there is a tiny hole in the silver metal below the brass. It gets overlooked frequently. When it is blocked, the engine will not stay idling for more than a few seconds, but will otherwise run fine if the throttle is kept open.