bro i have done cng tank service also, they loosed the tank out of car and drained all the oil out by turning the cylinders upside down, and then thy also serviced cng kit by taking it out frm bonnet and washing it with petrol and changing bearings, got this work done from hyundai workshop township.. those guys were seemed professional to me..
i have also done the tunning of car that included tapets and also service of throttle body..
now please guide which valve ur tawking about?????,
and after some research i have come to conclusion that i should change spark plugs (as i am using CHAMPION) and many ppl are telling they dont work good on cng and advising to get DENSO or NGK plugs + feul filter, i read in santro manual that it should be changed every 20,000kms and car is gng abt 100,000kms and i think its changed once and may b not changed at all (not sure abt it)..
