So in the below picture the larger pulley is a factory 20b pulley, the smaller one is a FC Atkins serpentine kit. I have 3 bolts to make sure the pulley bolt holes match. Timing is pretty far off...the car has a FC front cover on it as well.
Did Mazda move the needle on the front cover?

Which mark should I use? Im regretting not buying the John blanch tool to set TDC.

 

Well, I used the stock 20b mark on the larger pulley and it runs much cleaner. I'm gonna guess timing was too retarded before.

 

that's wild! glad you worked it out though.

do the 20Bs have an alternate method of locating TDC? you know, like on the 12As and 13Bs, the indent/flat area on the stock flywheel can be used if you need to.

 

I believe the 20b is just like the 13b where the keyway is at 9 o clock at TDC , the problem is if you have already assembled the motor you cant check where it sits in relation to the timing mark.

 

This is why I always scribe marks on stock hubs that follows the keyway so even if someone has put different pulleys on one of my engines there's a non-invasive way of getting very close to TDC - disassemble the pullies and do it visually.