Jelco Tk-850l tonearm counterbalance

I'm using a Soundsmith Zephyr MIMC ES star cartridge, when setting vtf the counterbalance is all the way at the end.  When I dial it in there is no way to secure it, sometimes as I'm putting on the dust cover it moves and I have to do it all again.  Something that would help is a heavier counterbalance.  If you have this tonearm and problem how have you dealt with this.  On the other hand I'm getting a lot of experience doing this, a little frustrated.

Thanks 
Mike