1980 Mazda 626 loses power when accelerator pushed to the floor.

Is there an easy way of determining the cause?

I can replace the carby for just $60AU with one from a wrecker,
however, I'll be wasting my time and money if the problem is
electrical.

The fuel filter is new and I've just finished putting the head back
after having it reconditioned (the power loss problem existed before
the head gasket blew).

Ken Johnson

I've just opened the throttle right up in neutral and this causes the
revs to vary between 2000 and 2500 rpm with the occasional backfire.

Am I right in thinking the problem could be electrical?

Ken Johnson