I own a civic 2000 with d16 auto tranny (cng). In morning i was driving it and was a lil harsh on throtel. [And some times on cng,due to air blockage in intake, vtec dont turns on and engine keeps on screaming without generating more power and rpm gets stuck between 5000 to 6000 .] after the drive when i stoped at a signal car turned off. I kept on starting it, after 3 tries it worked but my bad engine is now making some very loud "tak tak" sound when i rev it and this sound is directly propotional to rpm,although engine's performance is same and no problem but this sound ,and engine is generating black smoke too but very little. and just now i checked the engine bay there is a busted water pipe too and a leakage is very small . Well i wil be taking my car to honda site tommorow, right now i need some advice . What can be the problem? I am asuming some thing seriously wrong beneath the head or engine block.