B16 swap tach problems PLEASE HELP...

Hey guys and girls, I have a 94 civic that i had a mechanic who obviously doesnt know whats going on put in this engine b16. Now the problem is, I start the car and drive it easy, it runs fine, but I get on the highway and rev it to v-tech and the tach goes all wonky. it moves irratically in between its current revs. Does anyone know what the problem might be?

Note the guy kept the distributer from the old si engine d16z...let me know, thanks!

its either going to be a distributer problem or wiring

thanks a lot, i've considered buying a new distributor, but don't really dish out the money and find out that's not the problem. If anyone else has had this happen on your swap, please let me know what you've done. Thanks