Yes, I have that particular Zippers kit. Made for a decent bike in the winter time. Once the weather warmed up it was untunably bad; to the point of being unrideable.
Have found a solution that can be executed in just an afternoon's time though. Of course it involves having another set of pistons, cylinders and heads prepared and ready to go on in place of the poorly designed, poorly executed, unsupported and unwarranted product Zippers produced and provided. This needs to be done, however, after a prior afternoon's time has already been spent replacing the overly large cam they provide as part of this kit. The overly large cam they provide in an attempt to band aid the very poor head work.
Aside from the poor execution and compilation of the package the actual machine work on the heads I received was unbelievably poor as well. So, aside from the shoddy machine work, inexcusably poor service, badly designed head geometry and compilation of a package that didn't work for crap on my bike and at least two others I know of (necessitating eventually taking the whole mess off and starting over) I think it's a heluva package. In fact as long as you can avoid Zippers support or their product they're a heluva company.