Tachometer problem @ high RPM

My tach is bouncing all around when it gets to 5000 rpm or so.

Just wanted to know if anybody else has had this problem.

thanks

Mine does that when I launch at the track, and DBTBSS's speedo doesn't work till he lets out after making a pass. IDK why

I put a new inline fuel pump in and I grounded it to the frame.

I taped up the factory harness ground wire and tucked it up out of the way. Should I ground this wire to the frame? Would this ground wire have anything to do with the tach?