The carby sounds like a G4 or LM, both are interchangeable in their entirety but parts are not interchangeable between the two except for jets and primer faces.
If it only has the one long spring between the cap and the diaphragm then it will probably rev its ring off and the thottle will have little or no effect on engine speed. It sounds to me like its missing the 2nd shorter spring which goes on the other side of the diaphragm between it and the cam. If both springs are present then either the rubber diaphragm is not seated correctly, thus causing it to over rev due to the lack of vacuum or the vacuum hose going from the cap to the cowl is blocked or disconnected.
Make these simple checks and then we can begin to eliminate possible causes and troubleshoot as necessary.
The twins normally run the idle screw on the carb but this was dropped by victa on all their models some years later as it was more a gimmick than it was effective. People would turn them right down for a low idle and would ultimately cause premature plug failure and excess deposits in the head and exhaust. At the end of the day 2 strokes are made to work and not to be idled as it doesnt allow for the burning off of the oil in the fuel.
As for the catcher, good luck trying to source a decent one, but you never know, someone here may have one they're prepared to part with.
