i had similiar problem with my cultus... here are few tips try if it works for u
1) get your tappet adjusted... loose them
if problem still exists
2)try takin it to a electrician and get the current for Cng kit checked out
then there is the wrost case scenario
3) i had to replace my valve set and kit with a newer one which costed me alot then i expect but things turned out gr8... for this your engine would be dismentled till the head and will be sent to a leath machine wala for valve fitting.
hope this helps
And my car use to perform A-OKAY before i got the new Valve Kit!
regards