C4 Backfire

[lordkev1]

I have a 1984 C4 Crossfire Injection and have had it completely serviced and changed all fluids and plugs and filters etc.
When it is at idle and i rev it up I get a backfire but it drives great.
I am taking it back to the garage next week, but wondered if anyone has any thoughts please.

 

[Oneball]

Maybe an air leak, either in the inlet system causing a slightly off mixture or into the exhaust which will cause any unburnt fuel to detonate.

 

[lordkev1]

Thanks I will have it checkes