Vacuum erratic when electric fans turn on

[forestb]

A while back ago while I was adjusting my mixture screws on my quadrajet using a vacuum gauge I noticed that whenever my electric fan turned on I noticed that the vacuum would drop slightly and become less stable. Meaning that the needle would jump up and down. Is that normal? It doesn’t seem like it should be doing that. My only thought is that my fans are somehow effecting the power going to my distributor.