there is usually a small spring and a little shiny metal ball ,,,,this is for the two speed sytrifical clutch....

when the car is sitting in first gear the spring is open ---then as you start accelerating the the swing arm on the first gear begins pushing the little ball against the spring eventually the spring becomes pushed down enough to let the arm swing out and catch a little bar that allows the second gear to engage....if the screw was to tight it wouldnt allow the spring to move (there fore stuck in first)

if the set screw was to loose it would almost go right in to second....

there are two set screws i beleive one is to hold the gears on the shaft ,,,that screw should be down into a small notch on the shaft ..

LOCTITE both of these with BLUE loctite....this will help keep the screws gasketed in they will be able to be adjusted still to ..

depending on how much power your engine is putting out a different weight spring should be used to controll the shift..

NEVER bring your engine back to fresh setting unless you absolutely have to ,,,this cause different +temps to arise and that may cause
the chrome sleeve to stress,,,
small turns ,,most usually the setting on your engine when it was running fine is the good setting ,,,unless the weather gets cold then hot
or something like that ,,,

try a new glow plug sometimes this will not allow you engine to rev up high enough...

if none of this works ,,,hit me back i could keep goin and goin ,,,lol
tim