318 has developed a miss?

Or the amps drop when the RPM's go lower from the miss.:-)

Could be as simple as a fouling plug, but the pop out the carb would be something I would need to get to the bottom of.
Might have an intake valve hanging up and not closing intermittantly, or just a lack of fuel causing the pop back through the intake.

First thing I would do is pull the plugs and see if there is one that is significantly different than the other.
This would give you a starting point on which cylinder is acting up.