It doesn't need a 50cc pump. The 50cc pump uses pump cams specific to it, not the usual 30cc cams. If you have any cams w/three
positions and you are sure you have a 50cc pump, install that cam in position #3 and see if you have clearance. Otherwise you need 50cc cams.
IMO the best thing you could do is to tune the ignition advance, then put the 30cc pump diaphragm and cover back on it, w/the 30cc linkage, of course. Use a orange cam in position #1 and tune from there.
See post #49
for more on accelerator pumps.