Hoping someone out there may be able to help.

I just completed my kitfox's first runup and noticed that the engine is running very rough when I did my mag check on one of the mags.


When I did my mag check, "B" runs perfectly smooth with a slight RPM drop, but "A" runs very rough with a significant RPM drop.

I can't seem to find the cause of the problem.

In case it helps, the check was done at low RPMs simply as a preliminary check.