Lean condition recommendations
Backfiring through the intake is caused by a lean condition, but determining what causes it takes some diagnostic work. Rather than just replacing expensive items, you should get your hands on a Factory Service Manual which thoroughly explains the process of checking out the various components that make up the fuel injection system. After you have verified that the ignition timing is satisfactory, you should determine whether you have adequate fuel pressure by installing a fuel pressure gauge between the fuel filter and the fuel rail. A check of the fuel pressure regulator should come next. Then, the various fuel injection sensors and components can be checked by unplugging the fuel injection computer behind the left kick panel and using a multi-meter to diagnose at the connectors per the factory service manual. I was able to determine that I had a faulty air flow meter that was causing the lean condition in my '81 ZXT. The air flow meter can be opened up and adjusted if you know what you are doing. There is an adjustment under the sealed cover of the AFM to change the mixture of the fuel. Much is on file about air flow meters if you do a search at this site.
