300 rpm motor for VPI

Check the run-out on the 300pm motor pulley.  The pulley that came with my 300 RPM upgrade wobbled.  VPI replaced it. 

It seems like I saw some bass.  hearing more of my sub.  Maybe its run in issues

Agree with brf;  difficult to see how the motor could cause a channel imbalance.

However, I've found the Hurst motors to be very inconsistent;  I have some that are very noisy, others are near quiet, but they all exhibit vibration.  I believe the inconsistency is due mainly to the bearing design.

I've never been a fan of the 300 RPM motors.  Not only is the belt burn-out worse with the 300RPM pulley, but I also found that the 300 RPM motors to be noisier than the 600 RPM version due mainly to the higher power rating (7.5W for 300 RPM vs 5.5W for 600RPM in most cases):

http://www.diyaudio.com/forums/analogue-source/309925-hurst-motors-300-rpm-vs-600-rpm-upgrade-myth.html

Your new motor has nothing to do with what you are hearing, brf is right. Check your wiring, arm, cartridge alignment etc. as something got knocked out of whack. BTW, I have an HW-19 with a 600 rpm motor and a Prime with a 300 rpm motor and they both sound just fine to me. Don't let people discourage you about your new motor, it'll be just fine.

tzh21y, four years or so ago you posted a thread about your experience with going to the 300rpm motor and expressed dissatisfaction with the 300rpm motor due to increased noise; you decided to go back to the 600rpm motor. Is this the same unit that you are trying again?

I think that what you are hearing could, in fact, be do to the motor; especially if it is the same unit which may have issues. I think that the key may be your subwoofer. Question: where is your sub located relative to the main speakers? Contrary to popular opinion only the very lowest bass frequencies are, in fact, (mostly) non-directional. It is quite possible that if you have your sub positioned to the right of the soundstage that any low frequency noise, even if very subtle, that is being generated by the motor could skew the perceived balance in that direction. Did you try disconnecting the tt belt and turning on the motor with the stylus on a record to see which of the two motors is noisier?