tach showing wrong rpms!!

[parrotthead04]

I have a 2001 30 horse yamaha manual start. I baught a faria universal tach/hour meter and installed it. I hooked the sender wire to the extra wire comming off the rectifier ( i installed a rectifier kit bought from yamaha). The tach doesnt read the correct rpms. the most it will read is 4k. and I can tell from listening to it that its not correct. I set the dial on the back of the tach per instructions that came with it for that motor. Though the instructions say nothing about electric start or manual start. Then i tried some other settings on the tach and none seemed correct. What am I doing wrong?? I have emailed Faria but have got no reply yet.