I would say you pooped yourself out and since your gaining on your deads and squat those muscles are growing and kinda leaving your chest behind. Focus more on bench for awhile and kinda "cruise" with squats and deads and see what happens. Actually, I'd take a couple days off and get some good rest then start fresh. That may make a big diff.
BTW, I had an 87 LT500R I completely rebuilt then ended up selling it a year or so after it was done. Man I loved that thing. Now I gotta 99 scrambler 400 4x with a pipe and clutch kit, and wanna have it ported soon. But that zilla was a BAMF, to say the least, and wish I still had it.