Vy Gas problem ?

[Tiger28]

Hi there guys I have got a vy commodore series 2 I put on gas last year on June2011.It's a Prins system converter style.Lately when driveing on gas mainly when car is cold I get a flat spot where there is a loss of power and cant press the pedal not much at all, and if I do it will backfire. I then have to flip it on petrol were it runs fine without this problem.I'm also getting the check engine warning light on Gas only sometimes this was checked out and it was said gas is fine.I took in to to the Gas place who did it for me and told them the problem I had wth the flat spot and they changed the spark plugs which were pretty bad and thought that was the problem.Mixtures were fine to.He said it will be this likely,but see how you go before we change the leads.Can this be the problem the leads or is it something else as car runs fine on petrol ??.Thanks

[chevyshubox]

I would have done the leads at the same time as the plugs.
For some reason leads on gas cars have very short service life.

[Tiger28]

Might do that and see how it goes with changing the leads.Did it to me last night after work and car was cold.