underdrive pulley problem?????

[csfirefighter23]

I have a 91 s13 i put on a underdrive pulley and now when my car is at low RPM's I am having electrical problems, my alt. is not charging till i drive the car or rev the engine. I was wondering if the underdrive was causing the alt. to not spin fast enough to charge at low RPM's thanks for any info......

[TDS]

what kind of underdrive pulley did you get? Was it smaller than stock? Do you have a lot of electrical equipment (speakers, subwoofer, etc)? You sure your belt is not loose?

[1sikS13]

its called an underdrive pulley for a reason, upgrade to a quest alternator if it is a real problem, or have your alternator tested

[csfirefighter23]

yea the underdrive is alot smaller, the belt is tight but at idel it isn't charging i had it tested and it was good but im shure it spins it faster then my car at 700 rpm's thanks alot