With the limited info given,
I would start by checking the voltage at the battery while revving the engine to 4000rpms. Voltage should read 14 to 14.5 vdc. Any more or any less and you need a rectifier.
When you shut the engine off do you hear the rave valves cycle two times?
Are the plugs black and sooty?
There are several other checks you can do but you need a candoo pro.
Did you change anything else like the intake? TPS?