constraint problem

Hi I have problem with constraints, I made simple engine animation with piston and connecting rod, there is also big empty wich have ipo curve speed definied, but when I start animation (Ctrl+a) it’s looks horrible with fast speed, on slow looks good , piston and connecting rod don’t mach with each other
but when I rotate this big empty by hand it’s looks pretty good.
Anyone know how to fix it



SILNIK.blend (140 KB)