Is your head modded?? If so u can use the 38 pwk, the pj series sucks! I had one , if your head is stock use the 35pj , it will give u good bottom end , these motors 85-86 are half piston port an reed caged, aka bastard child design. I personally went from a stock motor an carb to a duncan power head an 36 pj fmf pipe to same head with different dome an a flowed 36 pwk = 37 , ported cylinder an in frame mhr pipe , that pj was a piece of turd , when I put my pwk on,what a huge power difference, it all depends on ur motor mods . Or just try each of them.