I bought a used SJ and the doser handle when I thwack away seems very stiff. When I watch videos online of other users whether professional or a home barista it looks very easy. Just quick thwacking with the finger tips. Is it just because I'm new at it and haven't built up the dosing muscles or is there a way of adjusting the tension?

The doser lever should advance without undue resistance. Not to ask the obvious, but is the bottom of the doser chamber clean? You did say it was used...

If the vanes don't appear to be hanging up, remove the two Allen screws holding on the bottom of the doser and check the handle itself. The thread Taking a Mazzer doser (completely) apart to clean includes good pictures. Note: Just in case you decide to disassemble the ratchet mechanism, pay particular attention to the warnings about using the vane arms for leverage; they break easily.

Cleaned the doser all out. Will check out the link and see how I can completely take the doser apart and see if there are old crusty grinds inside the mechanism making it tougher to dose. It's not extremely stiff, but not as loose as in the vids. No finger tips only dosing, I have to use my thumb to hold onto the doser chamber or the grinder will slip and slide all over the place.

You mentioned in the link that that level of disassembly was unnecessary. Assuming that, I guess I have cleaned everything else and the only solution I can think of was in the picture in one of the disassembly pictures.



I circled the spring, can I just unwind it a little and lighten up the tension? Anyone try that before with success?

You could try so, but I don't think that would solve the problem.
When I disassembled the doser of my Major, I found a lot of dirt underneath the lower doser star. I can imagine this can make the doser lever stiff.
Problem is the lower star is difficult to remove. You should first remove the roll pin. Don't try to jam the doser star with something, it seems like it breaks easily. I've used a wrench to take hold of the brass part and used a torque wrench to loosen the bolt. Mind you this takes a lot of force, but you won't harm the doser this way