First of all, get the settings done for petrol. Once all the issues are settled on petrol including missing/rough idling/rich mixture/spark timing, you can proceed with the settings on CNG. You just have to change only spark timing by rotating 15 degrees clockwise, but before that, make some marking on the distributor for it's petrol settings for reference. Also remember that do not fiddle with the petrol idle screw for the sake of cng setting to avoid such problems in future, the cng kit has separate idle and mixture settings for this purpose.
CNG setting is very simple, (if the engine is not starting on cng, start on petrol and then convert to cng) once engine is started rotate the throttle to half. Then start slowly tightening the power 'T' bolt clockwise until the engine starts hesitating. At this stage, start slowly rotating the screw anticlockwise until the engine starts running smooth (just 1 turn from the point of hesitation). Now check if the engine can rev with ease, if it shivers while giving throttle, just rotate the blot about 1/2 turn anticlockwise and tighten the nut at this point. If all this is done successfully, the mixture is set. Now check if the engine can do idling on cng, if the idling is rough, slowly rotate the idle screw clockwise and see if the idle improves. If it doesn't improve, slowly rotate the idle screw anticlockwise. Do this idle setting process until you get smooth idle. You can then check if the starting on cng issue is resolved or not. If the problem of starting and idling is still there, then probably spring under the idle bolt is problematic.