Lats start from one end
--- you are facing a pick up problem ; what all effects a cars pick up ?
-- clutch and pressure plates ; need a few simple tests to rule these out
-- weak ignition spark
--- coil ; generally a std issue with baleno for cultus i'm noy sure
-- HT leads ; need an electrician to check
-- plugs & gap. A plug with dark burns on ceramic part should be replaced, gap for cng cars is kept at 0.6 to .0.7
-- timing, if u r not using advancer keep timing at 18-20 degree for cng
-- valve clearance; i think it is 25/25 for cultus
-- A weak engine ; some people may disagree here but a weak engine gives a better pick up still u can check by talking dip stick out and look for any traces of engine blow
-- A head gas kit issue; open radiator cap and check for oil in water or water trying to spur out.
-- A choked carburettor : use carb cleaner spray first and go for carb servicing as your last option as an untrained procedure could put you further problems
-- Air mixture setting : two diffeent screws are used, one for petrol and one for cng
-- chocked or excessive air intake; self explanatory
-- chocked exhaust; the engine sound gives the clue
-- valve seats, in such case you should be having a higher temperature than usual
-- resistance on wheels; like swollen brake shoes or bearing issues but it should not affect the pick to a very significant level
I think i've listed all possible reasons. My personnel assessment is that you r having either of the three issues, carb circuit chocked, air choked or clutch or pressure plate problem