looks like the engine is weak now due to delayed or improper maintainance,its better not to spend so much cash on mods like plugs,intake,headers or exhaust but rather save up and buy a kabli engine for it,it wont cost much for the mehran,use the engine as long as u can and when it gives up then change it,its useless to spend soo much on mehrans 800cc engine when u can change the whole engine with a little cash added
*i saw a guy who had spent 18k on stage 1 mods and still got beated by a stock mehran
*therefor better to spend the money on a new engine like the 660cc turbo or g13b,which initially wod costs more but wod out-perform if compared to even moded cars like alto,santro,cultus